Unternehmensgruppe Theo Müller, the German yoghurt giant, switched targets in its efforts to beef up in the UK dairy market, unveiling a bid for Robert Wiseman Dairies – after buying shares in rival Dairy Crest.

Robert Wiseman Dairies, in a statement forced by a 19% rise in its share price on opening deals on London, said that is was in talks with Müller over a "possible cash offer".

The statement - which cautioned that there was "no certainty" of a deal, and that UK takeover rules gave Müller until February 10 to make up its mind on an offer – sent Robert Wiseman shares higher still.

The stock soared 43% to top 350p at one stage before easing back to end at 328p in London, up 34%, and adding well over £50m to Robert Wiseman's market value.

Previous speculation 

The announcement follows longstanding speculation that Müller prized a purchase of Dairy Crest, Robert Wiseman's bitter rival, in which the maker of Müllerlight and Müller Corner yoghurts bought a 3.0% stake in September 2010.

Dairy Crest said at the time that it had not received an approach from Müller, nor was soliciting offers.

"We've got a very good business and think we are doing a pretty good job by ourselves. We are happy where we are," March Allen, the Dairy Crest chief executive said then.

Robert Wiseman Dairies' main shareholders include members of the founding Wiseman family, who own well over 30%  between them, and First Milk, the UK's largest dairy co-operative, which two years ago sold down its stake to 10%.