Four top City law firms have made a huge pledge to back the bid for the 2012 Olympics by agreeing to write off their legal work for the company in return for association rights.

Clifford Chance, Freshfields Bruckhaus Deringer, Ashurst Morris Crisp and Berwin Leighton Paisner were named this week as the firms to provide people and legal expertise to London 2012 Ltd.

Ashurts, which has close links with bid leader Barbara Cassani, was the initial adviser in setting up the bid company, while Clifford Chance offered London 2012 its help.

Berwin Leighton was approached specifically for its planning expertise, and Freshfields was among those which responded to a request for interest from the company.

One-time Clifford Chance solicitor Charlie Wijeratna, now the bid's commercial director, said he struck deals with each firm that they will record and then write off their work up to a certain level, which he hoped not to breach.

He would not reveal the level of fees agreed, only saying the firms are 'very significant supporters of the bid'.

Mr Wijeratna said the bid had sought more than one legal adviser 'because we wanted to get a collective effort from the "big end" of town'.

He added that the firms provided credibility: 'The International Olympic Committee places a lot of emphasis on how prepared you are legally.'

In return, the firms will be recognised in London 2012's marketing programme and will receive certain 'rights of association' with the bid, which have still to be determined.

In the event that London wins the games, they will be organised by a separate company.

Mr Wijeratna acknowledged that working on the bid will give the four firms a level of expertise that could be of benefit when it came to that company seeking legal advisers.

However, he stressed that the firms had become involved because they recognised the benefit to London of winning the Olympics.

The legal work has been divided into four main areas: Freshfields is general corporate counsel and is also advising on commercial agreements; Clifford Chance is advising on IT, intellectual property, venue use, and sponsorship and marketing agreements; Ashursts on infrastructure projects and employment law; and Berwin Leighton Paisner on planning.

Secondees from the firms will join London 2012's in-house team.

Tim Jones, Freshfields' London head of corporate, said: 'By our commitment of resources, we hope to help London 2012 demonstrate to the International Olympic Committee that the bid is well supported by the business community.'

Others firms involved in the bid include London's Farrer & Co, which acts for the British Olympic Association, Birmingham-based Wragge & Co - advising the Greater London Authority - and City firm Denton Wilde Sapte, acting for the Department for Culture, Media and Sport.

By Neil Rose