After the financial crisis and the collapse of the Irish property bubble in the late 2000s, the Battersea Power Station site was bought by Malaysian investors, who subsequently contributed around £260m towards the construction of the Underground extension.

However, the subsequent development in the Vauxhall, Nine Elms and Battersea areas has been criticised for gentrification and low levels of affordable housing.

It is a Grade II* listed building, owing to its size, Art Deco interior fittings and decor, and design by architect Giles Gilbert Scott.

[4] There were various other proposals, including offices, a shopping centre and a new football stadium for Chelsea FC, as the site passed through several different owners.

Options assessed by TfL included upgrading nearby stations, extending London Underground lines to the site, as well as improving local bus routes.

[24] By November 2010, planning permission for the Battersea Power Station project had been granted by Wandsworth Council, with £203 million pledged by the developers towards a future extension of the Northern line.

[36] In October 2011, a report commissioned by Wandsworth Borough Council showed that the proposed extension had a positive business case, with the potential of delivering up to £4.5 billion in tax receipts across the area.

[37] In November 2011, Chancellor George Osborne announced that the UK Government would financially support the extension of the Northern line to Battersea, with the potential creation of an Enterprise Zone in the surrounding area.

[38][39] In December 2011, Treasury Holdings went into administration, after failing to repay debts of £340 million to Lloyds Banking Group and Ireland's National Asset Management Agency (NAMA).

[40][41] Due to the financial crisis and the collapse of the Irish property bubble, REO and Treasury Holdings had not been able to find an investor to allow them to proceed with the development.

REO had been criticised by investors and potential partners for their high levels of debt, as well as their "overly litigious" approach to business.

[42] Despite the sale of the site, Mayor Boris Johnson requested that the planning and development of the extension continue, with responsibility of the project passing to TfL.

[15] In March 2012, the Vauxhall Nine Elms Battersea Opportunity Area Planning Framework was published by the GLA, proposing 16,000 new homes, 500,000 square metres (5,400,000 sq ft) of commercial space and 27,000 new jobs across the area, as well as outlining the infrastructure requirements required to support this level of growth.

[50] Residents were also concerned regarding the potential levels of overcrowding at Kennington station, and TfL were considering if works were required to mitigate this.

[52] Funding for the extension was agreed with HM Treasury in 2012, with the use of tax increment financing and financial contributions by developers to pay back the construction loan over a period of 25 years.

[55][56] On 19 November 2013, the Secretary of State for Transport announced the start of a public inquiry to be conducted by an independent planning inspector, into the proposed construction of the extension.

[59] Points covered in the inquiry included that the extension would only serve one developer, that other alternatives (such as a route via Vauxhall) were not sufficiently tested, impacts on local Conservation Areas and Kennington Park, that an extension to Clapham Junction station should be built, as well as concerns regarding the levels of noise, vibration and dust during construction.

[59] TfL's responsiveness was also recognised, acting upon feedback to modifying the scheme to limit concerns, as well as adopting the most "stringent operational noise controls than on any other new underground railway in the UK".

[61] The extension was given the final approval by Secretary of State for Transport Patrick McLoughlin in November 2014, and was projected to open in 2020 at a cost of around £1 billion.

[62][63] In August 2014, Mike Brown, managing director of London Underground, announced that a £500 million six-year contract had been awarded to a joint venture of Ferrovial Agroman and Laing O'Rourke[64] to design and build the Northern line extension to Battersea, with Mott MacDonald as design engineer.

[83][84] In June 2019, it was announced that installation of track had been completed, and that an engineering train travelled the full length of the tunnel from Kennington to Battersea for the first time.

[126][127] Lambeth and Wandsworth Councils have estimated that around 20,000 new homes and 25,000 new jobs could be provided, and that the extension will support the "regeneration of the Vauxhall Nine Elms Battersea area".

[129] Transport in the local area has been improved, bringing rapid transit to communities currently served only by buses, as well as the more frequent trains than existing National Rail services from Battersea Park station.

[102] Furthermore, TfL state that the extension will reduce overcrowding on local bus services and at Vauxhall station, as well as on the Victoria and Northern lines.

[130][131] Other proposed works have included a new bridge across the River Thames to Pimlico and a planned rebuild of Vauxhall bus station.

[39][136] For the first time in England, tax increment financing will be used to pay back £660m of the loan, using future business rates from the development in the Vauxhall Nine Elms Battersea area, over a period of 25 years.

[39][139] Provision has been made for a future extension of the Northern line to Clapham Junction station, with a reserved course underneath Battersea Park.

[145][146] In March 2023, Mayor of London Sadiq Khan stated that the "case for an extension is not readily apparent, given Clapham Junction’s existing high levels of connectivity".

[147] In November 2024, Wandsworth Council announced that an initial feasibility study of an extension to Clapham Junction had been completed, and that there were "no physical engineering or geological constraints that would prevent the tube being extended".

[149][150] In 2018, plans to upgrade and rebuild Camden Town station were placed indefinitely on hold, due to TfL's financial situation.