Jaffa Cakes, Penguins and Nik Naks are among United Biscuits' snacks

Private equity groups Blackstone and PAI Partners have agreed to buy the company, with the deal expected to be completed by December.

United Biscuits, which was founded in 1948, employs more than 9,000 people, of whom about 7,500 work in the UK.

Other popular brands owned by United Biscuits include Jaffa Cakes, Penguin, Twiglets and Hula Hoops.

The purchase will be financed through a combination of equity contributed equally by US-based Blackstone and European firm PAI, as well as debt financing, the buyers said.

The deal is still subject to clearance by the European Commission and the UK Pensions Regulator.

In July this year, US food giant Kraft bought the Spanish and Portuguese operations of United Biscuits for �575m.

Union worries

"Blackstone has a successful track record of owning and developing companies such as United Biscuits and I believe the company will benefit from their involvement," said United Biscuits chief executive Malcolm Ritchie.

UNITED BISCUITS' UK BRANDS McVitie's Jacob's Cream Crackers Penguin Hula Hoops Twiglets Phileas Fogg KP Nuts Jaffa Cakes Skips Mini Cheddars

He added that United Biscuits was "delighted" that one of its existing shareholders, PAI - which has offices in Paris, London, Madrid and Milan - had decided to play a greater part in the business.

But unions were less happy, warning that a �320m deficit in the firm's pension fund was a key concern.

"Private equity deals are invariably struck for quick returns for shareholders," said Brian Revell of the T&G, which has some 900 members at United Biscuits.

"But the T&G's view is that the workforce and their pensions must be taken into account.

"That's why we believe there should be a cash injection, to show this is not a quick-fix deal but a longer term investment."

A spokesman for United Biscuits said the firm had already taken steps to manage its pension liability.

"We are committed to providing reasonable pension benefits to our employees and this commitment remains in place," the spokesman said.

"As part of the agreement with our new shareholders, a significant lump sum payment will be made to the pension plan and a commitment to an accelerated programme of contributions to cover the remaining deficit has been agreed."

Production shift

The news of the takeover came hours after United Biscuits announced it would be shifting production of its Nik Naks and Wheat Crunchies brands.

United Biscuits bought the brands from Golden Wonder in February and the snacks are currently made under contract at a factory in Scunthorpe.

It wants to make the products at its own factories in Teesside and Ashby-de-la-Zouch, Leicestershire. The move is expected to be completed by next year.