Freshfields Bruckhaus Deringer and Clifford Chance (CC) have taken the lead roles on the UK's biggest-ever single-site property deal – the £1.09bn sale and leaseback of HSBC's Canary Wharf headquarters.

CC acted for the acquirer, Spanish property group Metrovacesa, led by global real estate head Cliff McAuley and real estate partner Mike Edwards in the City, alongside Madrid-based real estate partner Alfonso Benavides.

Freshfields acted for HSBC, which received around 180 inquiries to buy the site, a 44-storey building that houses around 8,000 workers. HSBC agreed a 20-year leaseback of the building at an annual rent of £43.5m.

Real estate head Chris Morris led a team for the magic circle firm that also included senior associate Nick Leech.

The instruction is a coup for Freshfields' real estate team, which landed the appointment after a beauty parade in November.

The firm previously advised HSBC when it signed the original lease on the building around seven years ago but the latest deal represents its largest property deal for the client to date.

It is understood that HSBC previously handled most of its real estate work in-house before the bulk of its team joined Eversheds in Birmingham.

Allen & Overy advised HSBC on financing aspects of the deal.

Morris told Legal Week: "It was a fantastic and exciting deal for us to get. It was only on signing and seeing the number of zeros in the contract that it became clear how large the transaction was. When I started out [as a lawyer] £100m was an awful lot and to think that a building could be worth £1bn is mind-boggling."

The deal follows the approval earlier this week of the £1.5bn development of Silvertown Quays, which will eventually house Europe's largest aquarium. Ashurst property head Martin Wright advised Silvertown Quays, while Stephenson Harwood acted for the London Development Agency.

Linklaters advised Kajima Urban Development on the aquarium, with Scots firm McGrigors acting for funding provider Bank of Scotland.