Cadbury last month reported higher-than-expected sales for the third quarter, increasing pressure on Kraft to up its bid.

Analysts had said that Kraft, the maker of Oreo cookies, Nabisco crackers and its namesake cheese, needed to improve its original bid to have a chance at success.

Union unease

Speaking on Monday, Irene Rosenfeld, Kraft's chief executive, said: "We believe that our proposal offers the best immediate and long-term value for Cadbury's shareholders and for the company itself compared with any other option currently available, including Cadbury remaining independent.''

The US company said when revealing its previous bid in September that a merger with Cadbury would create a "global powerhouse", but there has been considerable opposition to the deal in the UK.

Felicity Loudon, the granddaughter of former Cadbury Brothers managing director Egbert Cadbury, said she was "particularly saddened by the possibility of one of the last remaining British icons disappearing into an American plastic cheese company".

In an attempt to appease unions, Kraft has pledged to save about 500 jobs at Cadbury's Somerdale chocolate factory in Bristol, southern England, reversing a decision by the British company's board to transfer production of chocolate at the plant to Poland.

But unions say they have not been given a detailed proposal on Kraft's commitments and point to the US company's decision to shut its Terry's Chocolate Orange factory in York, northern England, four years ago, transferring production to eastern Europe.