Allen & Overy (A&O) looks set for a fees windfall after landing the mandate to advise the administrator on the £2.6bn restructuring of struggling transport group Metronet.

The restructuring is the largest formal insolvency procedure ever seen in the UK and marks the UK's first ever public-private partnership (PPP) project to become insolvent.

Insolvency head Mark Sterling and restructuring partner Katrina Buckley are leading the team for A&O advising administrator Ernst & Young, a long-term client of the firm.

The process has handed roles to a number of firms, including CMS Cameron McKenna. The City firm has a longstanding relationship with Metronet, having advised on its initial £14.8bn PPP investment in the Tube network in 2003. Camerons projects partner Andrew Ivison is leading the team.

Herbert Smith head of projects Nicholas Tott and corporate recovery chief Kevin Pullen are advising Transport for London, which applied on behalf of the Mayor of London to have Metronet put into administration.

The move follows an extraordinary review of the company, which had requested £551m in emergency funding to continue operating but was granted just £121m. Metronet says it does not have access to funds to enable it to carry out its contractual obligations and announced it is going into administration last week (18 July).

Sterling commented: "With most deals, you have a pretty good idea on day one what the outcome will be. This is so unique that I cannot tell you what the position will look like in six months' time. It is exciting to do something very new."

Clifford Chance restructuring partner Mark Hyde is advising a collection of lenders, while Ashurst is advising Deutsche Bank as the security trustee and agent through restructuring chief Nick Angel and partners Nick Avery (projects) and Richard Kendall (finance). Ashurst advised the initial lending consortium on the 2003 project.

The project has five different groups of lenders and two separate public bonds. EIB is the senior debt provider. White & Case banking and insolvency partner Dan Hamilton advised the directors of Metronet.