Slaughter and May has won a role advising Arsenal Football Club on the high-profile sale of its captain Cesc Fabregas (pictured) to FC Barcelona .

The deal, which could be worth up to £35m, concludes one of the most protracted departures from a British premiership club, with Barcelona attempting to buy the Spanish national team star for several consecutive seasons without reaching a deal.

The five-year contract will see Barcelona, the club where Fabregas trained as a boy before joining Arsenal as a 16-year-old, pay €29m (£25m) to Arsenal for the player.

Because he is leaving before the end of his contract, Fabregas will also pay his former club €1m (£880,000) a year from his own salary for the initial contract period, while Barcelona has agreed to pay Arsenal €5m (£4m) if it wins the Spain's top football league, La Liga, twice and the European Champions League once during the five-year period.

Arsenal turned to Slaughters City corporate partner Andrew Jolly for advice on the complex arrangement.

Slaughters has a longstanding relationship with Arsenal and has advised the club on a number of high-profile deals including the £25m transfer of striker Emmanuel Adebayor to Manchester City in 2009.

Jolly also advised the club on setting up its 'Fanshare' scheme last year, which made portions of shares in the club available to supporters at affordable prices and saw Nabarro act for the Arsenal Supporters' Trust.

Barcelona could not be reached for a comment about any external legal advice.