The row between housebuilder Crest Nicholson and its biggest shareholder, Heron International, stepped up a gear this week as the London stock exchange’s takeover panel imposed a five-week deadline on Heron to state whether it was going to make a takeover bid.

In a statement on Tuesday, the panel said that after discussions with the advisers of both parties it had been decided that Heron must announce whether it intended to make a formal offer by 12pm on 4 May.

Two weeks ago Crest announced that it had received an approach from Heron, which has a 23.4% stake. However, Crest made it clear that the approach was unwelcome and that the price range of between 345p and 430p a share suggested by Heron was too low.

Heron, run by property entrepreneur Gerald Ronson, put pressure on Crest to open its books and said that the company had refused to brief it properly.

In response to the takeover panel’s demand, Crest chairman John Matthews reiterated the stance of the board on Tuesday. He said: “As a board we have our fiduciary duties to shareholders uppermost in our mind. We have already stated our view that Heron’s proposal significantly undervalues Crest Nicholson. We believe that it is in both shareholders’ and the company’s best interests that Heron should clarify its intentions.”

Heron repeated its demand for Crest to open its books.