Mayer Brown, CMS and Berwin Leighton Paisner (BLP) have secured top mandates on the £1.3bn sale of 20 Fenchurch Street, better known as the 'Walkie Talkie'.

The deal is the largest ever single-building transaction in the UK.

The building has been bought by LKK Health Products Group, a division of Hong Kong-based food company Lee Kum Kee Group.

Landsec, the UK real estate investment trust that owned 50% of the building, said it had exchanged contracts with the buyer today, while joint owner Canary Wharf Group has also agreed to sell its 50% stake to LKK.

CMS is acting for Landsec with a London team led by finance and regulatory partner Victoria Henry, alongside property partner Barry Morris and tax partner Nick Burt.

LKK has instructed Mayer Brown. The firm's team is being led out of London by real estate partner Chris Harvey alongside Jeremy Clay, Andrew Hepner, Caroline Humble, Anita Jones and Pat Jones.

The team also includes competition partner David Harrison, construction and engineering partner Jonathan Olson-Welsh, corporate and securities partners Jeremy Kenley, Connor Cahalane and Tim Nosworthy. Employment and benefits aspects of the deal are being handled by partner Nick Robertson. Transactions and consulting partner Sandy Bhogal is also involved in the deal.

BLP is advising Canary Wharf Group.

The Walkie Talkie is the fifth tallest completed building in the City of London.

The deal is the latest in a series of London property takeovers by Asian buyers. In May, the Leadenhall Building, known as the 'Cheesegrater', was sold for £1.15bn to Chinese property company CC Land.

Mayer Brown advised British Land on that deal alongside Herbert Smith Freehills, which advised Oxford Properties. BLP also acted on the deal, representing CC Land.