Ashurst and Clifford Chance (CC) have bagged lead roles on London's largest-ever office deal – advising on Beacon Capital Partners' acquisition of CityPoint for more than £650m.

The deal, which sees Ashurst advising real estate investor Beacon and CC acting for the selling consortium, exceeds February's £630m sale of the Gherkin to Germany's IVG Immobilien and investment bank Evans Randall.

It also represents an increase of more than £120m in little over a year for the sellers – Tishman Speyer, SITQ, Schroder Exempt Property Unit Trust and UBS Wealth Management – which paid around £520m for the building in January 2006. That deal saw UBS and Tishman buy in, with Schroders and SITQ keeping their stakes.

Ashurst real estate partner Hugh Lumby is advising Beacon, while CC is fielding two teams for the sellers using Chinese walls. One is acting for the consortium as a whole and the other acting individually for UBS.

Real estate partners Ian Morpeth and Sarah Thomas are acting for the consortium with another team, including associate Vanessa Collier, acting for UBS.

SITQ, the investment arm of Caisse de Depot & Placement du Quebec, turned to regular adviser Nabarro, which fielded a team under corporate real estate head Amanda Howard and newly-promoted partner Jonathan Cantor.

Schroders instructed Gibson Dunn & Crutcher with finance partner Tom Budd taking the lead role assisted by associate Oliver s'Jacob.

The line-up of firms is the same as it was for last year's sale of CityPoint by the City of London Office Unit Trust (CLOUT) to the consortium. That deal also saw Jones Day acting for CLOUT.

Beacon's acquisition took place over a month, exchanging on 4 April, and is expected to close in mid-May.

Howard, who has advised SITQ since it first invested in CityPoint in 2001, told Legal Week: "It was a very interesting deal and it was nice to see it go all the way through from acquisition to disposal."

The building houses a host of law firms, including Simmons & Simmons, Pinsent Masons and Simpson Thacher & Bartlett.