Proposals by architect Grimshaw for one of the largest freshwater aquariums in the world may have to be scrapped as the client decides this week whether to push forward with the scheme or quit.

The future of the £375m Nirah project in Bedford, which will be four times as big as the Eden project, has been in doubt since the project team ran out of money and the council declined to lend it more.

Client Nirah Holdings this week refused to accept a £300,000 loan from the council because it did not agree with the conditions attached to it. These include non-negotiable repayment terms and an commitment to submit a planning application by the end of next month.

Instead, the team called an emergency board meeting as Building went to press to discuss an alternative plan. Details of this were not available, but it is understood it does not involve scaling back the project.

A spokesperson for Nirah Holdings said: “There is a distinct possibility the project will not proceed. The conditions are completely unacceptable and we will not agree to them. Nirah Holdings faces a very difficult decision. After two years it is crunch time. We might have to decided to walk away from the whole thing now.”

If it goes ahead, the Nirah project will house up to 20,000 endangered species in artificially-created tropical conditions under an undulating roof in a 250-acre former claypit near Bedford.

Last month the crisis-hit project suffered a blow when project manager Ronnie Murning, who helped shape the Eden project, revealed he was about to quit.