Question: Which mutual building society, based in Leek, merged with a mortgage lending subsidiary of the cooperative bank in 2009?

full_context: Document 1: The Co-operative Banking Group: Co-operative Banking Group Limited (originally Co-operative Financial Services) was a UK-based banking and insurance company and a wholly owned subsidiary of The Co-operative Group. Established in 2002; its head office was located at the CIS Tower, Miller Street, Manchester.
Document 2: Nationalisation of Northern Rock: In 2008 the Northern Rock bank was nationalised by the British Labour Government, due to financial problems caused by the subprime mortgage crisis. In 2010 the bank was split into two parts (assets and banking) to aid the eventual sale of the bank back to the private sector.
Document 3: Co-operative Federal Trading Services: The Co-operative Federal Retail and Trading Services is the central buying group for co-operative retail societies in the United Kingdom. It came into its current structure in 2015, though its predecessor was established in 1993, and it supplies almost all food bought for sale by the over 4,000 co-operative foodstores in the UK. The buying group is owned and controlled by each of its member societies but is managed by The Co-operative Group on their behalf. It operates by pooling the collective £8.5bn buying power for 18 co-operative societies in the UK, allowing them to negotiate better prices from suppliers, so as to compete effectively with other UK supermarket chains.
Document 4: Northern Rock: Northern Rock, formerly the Northern Rock Building Society, was a British bank. Based at Regent Centre in Newcastle upon Tyne, United Kingdom, Northern Rock was originally a building society. It demututalised and became Northern Rock bank in 1997, when it floated on the London Stock Exchange with the ticker symbol NRK. During the early 2000s the company borrowed substantially to fund mortgages, with the aim of ambitious growth, and also donated large amounts to charitable purposes and communities directly and through sponsorships. The global banking crisis beginning around 2007–2008 meant that it was unable to produce income as expected from its loans, and was at risk of being unable to repay the amounts it had borrowed. The news that the bank had approached the government for support with its liquidity led within 24 hours to a public lack of confidence and concerns that savings were at risk, and the bank failed following a bank run as people rushed to withdraw their savings. It was the first British bank in 150 years to fail due to a bank run.
Document 5: National &amp; Capital: National & Capital, or N&C as it is more commonly known claims to be "one of the UK's leading mortgage brokers" who specialise in the placement of prime, buy to let and non-conforming mortgages. It was established in 1999 as Fasttrack Finance but later changed its name to Essex & Capital Mortgage Corporation Ltd when it was acquired by the US Investment Bank Bear Stearns. It was taken back into private ownership in 2006 as National & Capital when Bear Stearns took the decision to withdraw completely from the UK mortgage market after a rise in foreclosures in the United States in late 2006 which subsequently triggered a global financial crisis through 2007 and 2008.
Document 6: Mortgage industry of the United Kingdom: The Mortgage industry of the United Kingdom has traditionally been dominated by building societies, but from the 1970s the share of the new mortgage loans market held by building societies has declined substantially. Between 1977 and 1987, the share fell drastically from 96% to 66% while that of banks and other institutions rose from 3% to 36%. The major lenders include building societies, banks, specialized mortgage corporations, insurance companies, and pension funds. During the four years following the Financial crisis of 2008 the UK mutual sector provided approximately 80% of net lending to the housing market. There are currently over 200 significant separate financial organizations supplying mortgage loans to house buyers in Britain of which the Lloyds Bank and the Nationwide Building Society have the largest market share.
Document 7: The Co-operative Group: The Co-operative Group, trading as The Co-op, is a British consumer co-operative with a diverse family of retail businesses including food retail; electrical retail; financial services; insurance services; legal services and funeralcare, with in excess of 4,200 locations. It is the largest consumer co-operative in the UK and owned by more than 4 million active members. Membership is open to everyone aged 16 and over in the society, provided they agree to subscribe £1 sterling in the capital of the society out of their first share of the profits and share the values & principles upon which the group was founded. Members are democratically involved in setting business strategy, decide how social goals are achieved, and share in its profits - in the 2016 £19m was returned to members and their chosen local community causes via the 5+1 scheme. No year end dividend was paid in 2015.
Document 8: Britannia Building Society: Britannia was a mutual building society in the United Kingdom. It had its headquarters in Leek, Staffordshire, and was the second largest building society in the UK based on total assets of £36.8 billion at 31 December 2007. It became an important provider of both mortgages (including subprime mortgages through its Platform Home Loans subsidiary) and savings, as well as commercial lending.
Document 9: Portman Building Society: The Portman Building Society was a mutual building society in the United Kingdom, providing mortgages and savings accounts to consumers and offering loans to commercial enterprises. Its head office was in Bournemouth and its administration centre in Wolverhampton. Portman merged with the Nationwide Building Society in August 2007, at which time it was the third largest building society in the UK and the largest regional building society in the south of England, with 154 branches and assets exceeding £15 billion.
Document 10: Building society: A building society is a financial institution owned by its members as a mutual organization. Building societies offer banking and related financial services, especially savings and mortgage lending. Building societies exist in the United Kingdom (UK), and used to exist in Ireland and several Commonwealth countries. They are similar to credit unions in organisation, though few enforce a common bond. However, rather than promoting thrift and offering unsecured and business loans, the purpose of a building society is to provide home mortgages to members. Borrowers and depositors are society members, setting policy and appointing directors on a one-member, one-vote basis. Building societies often provide other retail banking services, such as current accounts, credit cards and personal loans. The term "building society" first arose in the 18th century in Great Britain from cooperative savings groups.
Document 11: The Cambridge Building Society: The Cambridge Building Society is a UK mutual building society based in Cambridge, Cambridgeshire, England. It is the 14th largest in the United Kingdom based on total assets of £1,128 million at 31 December 2015. It is a member of the Building Societies Association. The Society was formed in 1850 as the Cambridgeshire Permanent Benefit Building Society, adopting its current name in 1945. There is no connection between this Society and the Cambridge Foresters’ Benefit Building Society which was dissolved in 1960 or the Cambridge Peers Economic Building Society which was dissolved in 1972.
Document 12: Suomen AsuntoHypoPankki: Suomen AsuntoHypoPankki is a Finnish bank specialized in mortgage lending. The parent company of Suomen AsuntoHypoPankki is The Mortgage Society of Finland, a building society established in 1860. The Mortgage Society has more than 10,000 members.
Document 13: Platform Home Loans: Platform Home Loans is the intermediary mortgage lending subsidiary of The Co-operative Bank. The current incarnation of the firm was launched in February 2003 following the merger of Britannia Building Society subsidiaries Platform Home Loans and Verso. The firm became part of the Co-operative Bank group when that firm merged with Britannia in 2009.
Document 14: Shamrao Vithal Co-operative Bank: The Shamrao Vithal Co-op. Bank Ltd. (SVC Bank) known as SVC Cooperative Bank Limited, established in 1906, is one of the oldest Urban Co-operative Bank in India. The bank was founded when co-operation was just started to begin in the country. It was set up with the primary objective of assisting the less fortunate members of the community in its economic enterprises. This was also to encourage savings and to create funds for providing financial aid to deserving members.
Document 15: Abbey National: Abbey National plc was a bank based in the United Kingdom and former building society, which latterly traded under the Abbey brand name. As the former Abbey National Building Society, it was the first building society in the United Kingdom to demutualise, doing so in July 1989. The bank expanded through a number of acquisitions in the 1990s, including James Hay, Scottish Mutual, Scottish Provident and the rail leasing company Porterbrook. Abbey National launched an online bank, Cahoot, in June 2000.
ground_truth: Britannia Building Society