Successor to the UK Trident system The Successor programme refers to the replacement of the existing UK Trident programme of submarine - launched nuclear missiles . This would involve replacing the " Vanguard " class of four Trident ballistic - missile armed submarines with a new class designed to continue a nuclear deterrent after the current boats reach the end of their service lives . The government has begun planning a new submarine - based system but there is opposition from those who want to take the opportunity for full nuclear disarmament or replacement with a cheaper , less capable nuclear weapon delivery system . On 18 May 2011 the British government approved the initial assessment phase for the construction of new Trident submarines . The term " Trident " is widely used to refer to Britain ' s entire current system of nuclear weapons , including the relevant submarines , missiles and warheads . " Trident " is also the shortened name of the system ' s submarine - launched ballistic missile , the UGM - 133 Trident II D - 5 . Background . Policy . Official policy regarding nuclear weapons is for use as a defensive nuclear deterrent . This refers to the possession of nuclear weapons to deter an enemy nuclear attack with the threat of a retaliatory second strike . The current reasoning of deterrence is explained in the 1998 Strategic Defence Review ( SDR ) : Since the Manhattan Project produced the first nuclear weapons during World War II , the UK has worked closely with the United States on nuclear strategy . This cooperation was formalised in the 1958 Mutual Defence Agreement ( MDA ) and has been a key aspect of the special relationship between the two countries . Trident system . Since the retirement of the last Royal Air Force WE . 177 nuclear bomb in 1998 , the British nuclear system has been wholly submarine - based . This is intended to deter a potential enemy because they cannot ensure eliminating the entire stockpile in a first strike if a ballistic missile submarine ( Ship Submersible Ballistic Nuclear or SSBN ) remains undetected . Since the Strategic Defence Review , the UK has maintained a stockpile of around 200 warheads . In a policy known as " Continuous at Sea Deterrence " , at least one " Vanguard " class SSBN is kept on patrol with up to 16 Trident missile s sharing up to 48 warheads from the stockpile at any given time . The SDR considered this was the minimum number of warheads adequate for deterrence . It is collectively known as the Trident system . The majority of this system is based in Scotland at HM Naval Base Clyde , which includes the Faslane home of the " Vanguard " submarines , and at the Coulport nuclear depot . The oldest submarine of the " Vanguard " class is expected to remain in service until 2017 without a refit , prompting consideration of a replacement before the end of 2010 to allow for development time . Replacement system . Proposal . A December 2006 Ministry of Defence white paper recommended that the nuclear weapons should be maintained and outlined measures that would do so until the 2040s . It advocated the currently preferred submarine - based system , as it remained the cheapest and most secure deterrence option available . Costs for this option are estimated at £15 – 20 billion based on : These 2006 / 7 prices would equate to about £25bn in out - turn price for the successor submarines ; the 2011 Initial Gate report confirmed estimates of £2 - 3bn each for the warheads and infrastructure . These cost estimates exclude the " Vanguard " 5 year life extension and decommissioning , and it is unclear if new Trident missiles will need to be purchased for the life extension programme . Running costs would be about £1 . 5 billion per year at 2006 prices . On 18 May 2011 the British government approved the initial assessment phase for the construction of new Trident submarines , paving the way for the ordering of the first long - lead items and preparations for the main build to begin in the future . The new submarine class will retain the current Trident II missiles , and will incorporate a new ' PWR3 ' nuclear reactor as well as technology developed for the " Astute " - class SSNs . The final decision on whether to build the Successor submarines will be taken in 2016 and the first boat will be delivered in 2028 . Trident D5 missile life extension . In 2002 , the US Navy awarded a contract for the Trident II D5 Service Life Extension Programme to extend the life of the missiles from the mid - 2020s to about 2042 , to match the extended life of the US . The UK will join this programme to arm a " Vanguard " submarine class replacement . Submarines . The paper suggested parts of the existing Trident system be refitted to some extent to prolong their lives . However , the relatively short ( five years ) life extension potential of the " Vanguard " class meant that a new class of SSBNs should replace it in the early 2020s . There are suggestions that the new fleet be cut to three hulls if a Continuous at Sea Deterrent patrol could still be assured at that number . The first SSBN would take 17 years to be designed and built , making a five year life extension of the " Vanguard " class necessary . On this basis , a refitted " Vanguard " class could still shrink by at least one vessel before the first replacement SSBN enters service . Both BAE Systems Submarine Solutions and Rolls - Royce Marine Power Operations are undertaking design studies for the new submarine class . BAE presented two designs at DSEi 2007 labelled Concept 35 and Advanced Hull Form ( AHF ) . Concept 35 is an evolution of the " Vanguard " - class with influences from the " Astute " - class . Advanced Hull Form is a less conservative design which , rather than a standard tapered design of the stern , features a Y - shaped stern which houses much of the boat ' s machinery outside of the pressure hull . Power plant . In March 2011 a safety assessment of the current Rolls - Royce PWR nuclear power plant design , by the Defence Nuclear Safety Regulator in November 2009 , was released under a Freedom of Information request . The Regulator identified two major areas where UK practice fell significantly short of comparable good practice , loss - of - coolant accident and control of submarine depth following emergency reactor shutdown . For the replacement submarine the option of developing a new PWR3 plant based on current US design is under consideration , and in March 2011 Defence Secretary Liam Fox indicated this was the preferred option " because those reactors give us a better safety outlook " . In May 2011 the Ministry of Defence announced that the US design had been selected for the PWR3 , at a cost of about £3 billion . Munitions . The 2010 Strategic Defence and Security Review concluded that the Successor submarine would have eight operational missiles carrying no more than 40 operational warheads between them . This would allow the UK to reduce its stocks of operational warheads from 160 to 120 , and the overall stockpile from no more than 225 to no more than 180 . They would be carried in a 12 - missile common missile compartment designed in collaboration with the US for their SSBN - X , which could accommodate the current Trident D5 missiles and any replacement missile once the D5 reaches the end of its expected life in the 2040s . The remaining warheads are expected to last until the mid - 2020s , with a decision to either replace or refurbish them taken closer to that time . The government - owned nuclear weapons research company Atomic Weapons Establishment would likely play a key role in either , with over £1 billion being invested between 2005 and 2008 to maintain " key skills and facilities . " The replacement of the Trident missiles was also deferred , as the UK intends to participate in a US programme to lengthen the missiles ' lives from the 2020s through to the 2040s . Alternatives . The Royal United Services Institute ( RUSI ) , a British defence and security think tank , released a paper in July 2010 assessing " four possible options for maintaining both an effective nuclear deterrent and also reducing costs in light of anticipated budget restrictions . " These proposals were motivated by the fact that funding for the Trident renewal programme must now come from the core MoD budget . The paper outlined four options consistent with the purposes of cost reduction : The paper concludes that " given the opportunity costs for conventional capabilities that current plans for Trident renewal are due to incur over the next decade . . . there is now a growing case for a re - examination of whether there are less expensive means of pursuing this objective . A key element of such a review is likely to be a reconsideration of the need to maintain a commitment to CASD in strategic circumstances that are now very different from those in which it was first introduced . " In July 2013 , the British Government published the Trident Alternatives Review . Its findings including : - Parliamentary support . On 14 March 2007 , the Labour government won Commons support for the plans to renew the submarine system . The proposals were passed by the House of Commons by a majority of 248 . Despite a clarification that the vote was just for the concept stage of the new system , 95 Labour MPs rebelled , and it was only passed with the support of the opposition Conservative Party . It was the first time MPs had been given the chance to vote on whether the UK should remain a nuclear power , and the biggest backbench rebellion since the beginning of the 2003 Iraq war . The Labour government decided the final decision to manufacture should be made in 2014 . The new 2010 coalition government agreed " that the renewal of Trident should be scrutinised to ensure value for money . Liberal Democrats will continue to make the case for alternatives . " Research and development work continued with an ' Initial Gate ' procurement decision , but the ' Main Gate ' decision to manufacture a replacement was re - scheduled for 2016 , after the next election . In May 2013 it was reported that Whitehall ' s forthcoming Alternatives Review had found that land , air or cruise missile systems would be more expensive or more impractical than Trident , and that there would be little saving in reducing from 4 submarines to 3 . Cutting to two submarines would cut the capital cost by up to £5bn and save nearly £1bn / year in running costs , but would mean that continuous patrols were no longer possible . The Liberal Democrats , minority partners in the ruling Coalition government , appeared to favour this 2 - boat Trident option whilst their Conservative partners preferred the 4 - boat option , quoted as costing £20bn . The review found that participating in the US Trident programme was cheaper than starting a UK - only cruise missile programme , previously the Liberal Democrats ' preferred option . Academic review . The Bradford Disarmament Research Centre has received funding from several anti - nuclear organizations , including the Joseph Rowntree Charitable Trust , for a review of the Government ' s reasons for replacing Trident , aiming " to transform the intellectual agenda on Trident replacement through a detailed and critical examination of the government ’ s rationales for Trident replacement , a number of crucial issues excluded by the government and the wider implications of the decision , which require a full and balanced . " Opposition . Morality . The possession of nuclear weapons , as a form of weapons of mass destruction , has long been criticised in British politics for being immoral , by members of the Campaign for Nuclear Disarmament and their supporters . As such , it has been at the core of the peace movement in the UK since the first introduction of nuclear weapons in the 1950s . The Campaign for Nuclear Disarmament has historically been a significant anti - nuclear lobby group since its formation in 1957 . As a result , the potential replacement of Trident has naturally been criticised by the CND , coming under their " Scrap Trident " campaign . More recently in 2006 , 20 bishops claimed Trident was " anti - God . " Other religious leaders , including former Archbishop of Canterbury Rowan Williams , have questioned the morality of replacing Trident . Other groups claim the development of new nuclear weapons would undermine Britain ' s stance with other countries , such as Iran and North Korea , and international nuclear disarmament in general . The UK government insists that there are no plans to enhance the capability of the missiles in terms of payload , range or accuracy , in order to avoid such diplomatic problems . Strategic value . Another reason cited is the claim that the nuclear environment has become less dangerous since the development of the deterrent during the Cold War . Consequently , with a diminished nuclear threat towards Britain , the value of having a deterrent to guard against it has fallen as well . The Ministry of Defence has a declared policy of sub - strategic use which would see , for example , a limited nuclear strike ( e . g . one missile with one limited yield warhead ) used as either a deterrent to a country from using chemical or biological weapons or as retaliation for having used them . Outspoken critics on this basis include former politicians Denis Healey and Michael Portillo . Cost and timing . Several groups , such as the Liberal Democrats , Plaid Cymru , Green Party of England and Wales and Scottish National Party and some trade unions , prefer the money to be spent on public services or improved equipment for conventional forces . Greenpeace has claimed the recent £1 billion investment in AWE is for secret initial work on developing a replacement . In evidence to the House of Commons Defence Select Committee on 23 January 2007 , the US nuclear expert Richard Garwin said that the plans were " premature and wasteful " , and that delaying the decision for 15 years following inexpensive engine repairs would save £5bn . He added that pressure to commission a new fleet of submarines was rooted in the shipbuilding industry ' s urge to land lucrative contracts .