The sale of Alliance Boots has taken a step closer to a £12 billion competitive auction after the Wellcome Trust joined forces with Terra Firma to ask Britain’s biggest chain of chemists to open its books to a rival bidder.

The charity and the private equity firm have put in a combined request to carry out due diligence. They expect a response by the end of this week.

An approach would pit them against a bid consortium of Kohlberg Kravis Roberts (KKR), the global private equity group, and Stefano Pessina, the Alliance Boots deputy chairman and its largest shareholder.

Alliance Boots is expected to make a decision by Friday on whether to accede to the latest request for access to its books, even though the new stalkers have not yet put together financing, which needs to top KKR’s offer of £11.4 billion.

A source said: “They can’t line up funds without access to the books but are already talking to a few potential advisers.”

The trust, Britain’s biggest charity, and Terra Firma, which is led by Guy Hands, the high-profile financier, are seen as credible potential buyers.

Alliance Boots has been in play since March 9, when it emerged that KKR and Mr Pessina had offered £10 per share for the retail-and-wholesale group. The bid raised concerns over conflicts of interest on the board and fears among shareholders that the deputy chairman, who owns 15 per cent of the company, had discovered a “pot of gold” in the business of which they were unaware.

The Alliance Boots board agreed on March 30 to give KKR and Mr Pessina access to the company’s books for a limited time to undertake due diligence, after the consortium raised its initial bid for the group to £10.40 per share, valuing the company at £11.4 billion.

At the time, the board said that it would allow any credible bidder similar access.

Sources said that the Terra Firma team had not yet come to a firm decision on whether to make an offer, and that they were aware that the KKR consortium was “a long way ahead” in the process.

Meanwhile, Celesio, the German pharmaceutical group that is also looking at a possible bid for parts of Alliance Boots, is not thought to have attracted private equity backing for an approach yet.

The prospect of a viable alternative offer is likely to please shareholders, some of whom have been concerned by the value put on the company by KKR and Mr Pessina, as well as the deputy chairman’s seemingly sudden decision to abandon a public listing.

His plans to take the company private came less than nine months after the company was created through a £7 billion merger of Boots and Mr Pessina’s Alliance Unichem. At the time of the merger, Mr Pessina wooed investors with his vision for a strong European group, with growth to be fuelled by his excellent contacts and long-term commitment to the company.

The group has about 2,600 healthcare stores in the UK and a further 400 overseas.

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