More than ten banks are understood to be competing with each other to fund Terra Firma's counter-offer for Alliance Boots and are willing to lend nearly twice the £11.4 billion price tag attached to the pharmacy chain. But tension is mounting between rival contenders over the range of due diligence information being made available.

It is understood that Terra Firma is concerned about what it sees as limited information from Alliance Boots which comprises a couple of boxes of documents.

There are also fears that Terra Firma is at a disadvantage compared with its rival, Stefano Pessina, the deputy chairman of Alliance Boots, who is bidding with the backing of KKR, the private equity firm.

Mr Pessina and KKR have indicated a £10 billion offer for the company. Commenting on due diligence, a spokesman at Alliance Boots said: "We have fulfilled all the legal obligations we have to the bidders."

Although Mr Pessina, as Alliance Boots' deputy chairman, is precluded from any activities that are connected to his KKR-backed approach for the business, an Alliance Boots' spokesman said Mr Pessina is still engaged on "strategy work" for the business.

He said: "He remains a director of the company and continues to fulfil his executive responsibilities but that does not include any matters connected to the approach."

Mr Pessina and Alliance Boots' board have mutually agreed that he should not visit the company's head quarters during the bidding process.

Terra Firma gained access to Alliance Boots' accounts on Saturday and, with a staff of 100 people, has been working throughout the weekend on the deal. Terra Firma first approached Alliance Boots' board on Thursday, April 5 and signed the confidentially agreement allowing it access to the company's accounts on Friday, April 13.

The private equity firm run by City financier, Guy Hands, will choose a bank this week to fund its bid for Alliance Boots. Prospective lenders are believed to be putting together debt financing of up to £20 billion. An announcement on which bank has won the mandate is expected later this week.

The firm has teamed up with the Wellcome Trust, Britain's largest medical research charity, to make the bid.

Terra Firma is currently undergoing due diligence after requesting information under rule 20.2 of the UK Takeover Code which states that any information that is provided to one offeror must, on request, be given "equally or promptly" to another bidder "even if that offeror is less welcome".

Mr Pessina and KKR could make a formal bid for Alliance Boots as early as this week. By this Friday, April 20, Mr Pessina and KKR will have spent three weeks engaged in due diligence on Alliance Boots.

Terra Firma and the Wellcome Trust are entitled to continue due diligence even if their competitors table an offer.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive