https://en.wikipedia.org/wiki/Web_blocking_in_the_United_Kin...

Excerpts:

"Websites and services are blocked using a combination of data feeds from private content-control technology companies, government agencies, NGOs, court orders in conjunction with the service administrators who may or may not have the power to unblock, additionally block, appeal or recategorise blocked content."

"The technical measures used to block sites include DNS hijacking, DNS blocking, IP address blocking, and Deep packet inspection, making consistent verification problematic. One known method is ISP scraping DNS of domains subject to blocking orders to produce a list of IPs to block."

"There is a private agreement in principle between leading ISPs and rights holders, made with encouragement from government, to quickly restrict access to websites when presented with court orders. The court orders are not made public and "overblocking" is sometimes reported"

"In 2019 an in-depth investigation into overblocking by the Open Rights Group and digital privacy site Top10VPN.com found that thousands of websites were being incorrectly blocked. These included relatively harmless example from industries such as wedding planning and photography, to more damaging and dangerous mistakes like official websites for charities, schools and mental health support."

"Cleanfeed originally targeted only alleged child sexual abuse content identified by the Internet Watch Foundation. However, no safeguards exist to stop the secret list of blocked sites being extended to include sites unrelated to child pornography. This had led to criticism of Cleanfeed's lack of transparency which gives it considerable potential for broad censorship. Further, Cleanfeed has been used to block access to copyright-infringing websites after a court order in 2011 required BT to block access to NewzBin2.[30] This has led some to describe Cleanfeed as the most perfectly invisible censorship mechanism ever invented and to liken its powers of censorship to those employed currently by China."

"The Counter Terrorism Internet Referral Unit (CTIRU), which was set up in 2010 by the Association of Chief Police Officers and run by the Metropolitan Police Service, maintains a list of sites and content that in their opinion incites or glorifies terrorist acts under Section 3 of the Terrorism Act 2006. This list is passed to the public estate institutions so that access to the sites can be blocked. ISPs BT, Sky, TalkTalk and Virgin Media incorporate the CTIRU block list into their filters. The CTIRU also issues removal requests if the Internet content is hosted in the UK. The UK is the only country in the world with such a unit."

"In response to the increasing number of file sharing related blocks, a number of proxy aggregator sites, e.g. torrentproxies.com, have become popular. In addition to the following, proxy sites designed to circumvent blocks have been secretly blocked by ISPs, driving users to proxy comparison sites. [...] On 5 August 2014, City of London Police Intellectual Property Crime Unit arrested a 20-year-old man in Nottingham on suspicion of operating a proxy server that allowed internet users to bypass blocks on many popular sites."