Union leaders are calling on Patricia Hewitt, the Health Secretary, to intervene in the takeover tussle at Boots and demand assurances that a successful private equity bid will not harm the NHS.

The call comes as Stefano Pessina, Alliance Boots’s vice-chairman, together with his backer KKR, prepares to launch a formal £11.4 billion offer for Boots next week, having finished examining the health and beauty company’s books. KKR and Mr Pessina are expected to approach the Boots board towards the end of next week, seeking a recommendation of their £10.40 a share bid.

A rival group, made up of Terra Firma Partners and Well-come Trust, the medical research charity, is firming up financial backing for a potential counter-bid.

In a letter, Paul Kenny, the GMB general secretary, said that more than 100 village pharmacies could be closed to cut costs if Alliance Boots is “loaded up with debt”.

Mr Kenny has also called on Ms Hewitt to ensure that any successful bidder does not securitise the income from more than £1 billion of NHS contracts held by Boots to fund a takeover. In the letter, Mr Kenny wrote: “GMB members would like you, one of Boots’ largest customers, to call in Stefano Pessina to ask him, as a major supplier of medicines to the NHS, how the sums add up for the taxpayers.

“GMB members would also like to know how many hundreds of their local pharmacies will be forced to close to pay the interest bills.

“Boots profits for the year to the end of March 2007 are projected to be around £480 million. The interest payments on £7 billion of debt that may be taken out to fund the purchase could amount to more than £500 million per annum.”

The letter is the latest attack by the GMB on private equity since stepping up its campaign when CVC admitted it was considering a takeover attempt of Sainsbury’s in February.

A spokesman for the bidding consortium said that its initial announcement made clear that it was a long-term investor with a vision based on growing the business. He said: “KKR and Mr Pessina have a tremendous track record in making long-term investments.”

Times Recommends

• C&G axed - 1,660 jobs to be lost
• UK house prices rise 1.1% as buyers return
• Mixed reaction to US banks repaying bailouts