The Government's chief advisers on heritage and the environment have ruled out supporting Frank Gehry's £290 million plans for the seafront.

English Heritage and the Commission for Architecture and the Built Environment (CABE) - between them the guardians of much of England's public space - said the King Alfred sports and housing complex would not fit in with the rest of Hove seafront.

It was also claimed that the development - which would include a £36 million sports centre, shops, cafes, bars and restaurants - would be too difficult for the public to get into.

Critics claimed last night the shock announcement had effectively sounded the death knell for the controversial project.

Garry Peltzer Dunn, leader of the Conservative group on Brighton and Hove City Council, said: "It is almost inconceivable that a local authority would go against the advice of English Heritage and CABE on a plan like this."

The blow came as Mr Gehry unveiled £1 billion plans to build a 50 storey glass-encased skyscraper in Los Angeles with plans to start construction by the end of the year.

It is the second major setback the King Alfred has suffered in a week after the District Valuation Office - an arm of the Inland Revenue - announced that Karis's plans for finanancing the project did not add up.

And it marks an extraordinary about-face for CABE, which announced its support in November last year for the King Alfred.

Andy Brown, south east director of English Heritage said: "We have had long discussions with the applicants and it got to the point where the council wanted either a 'yes' or a 'no' from us and as the plans stand we have had to say 'no'.

"We believe there is a good scheme in there waiting to get out but at the moment we have a number of issues which we cannot give our backing to."

The major sticking points were:

l The scale of eight smaller perimeter blocks of apartments, which both organisations said would be out of place.

l A failure on the part of the designers to ensure the buildings were "organic" and would be seen as an integral part of Hove.

l Criticism over the "public realm" part of the design - the public access to the site.

Valerie Paynter, of Save Hove, a group of activists opposing the project, said: "It's another nail in the coffin. It is unravelling before our eyes."

Neither advisory group said it had a problem with the two tallest towers dominating the development, which include 754 luxury and affordable flats.

But English Heritage said last night it had notified the council of its disapproval of the plans in their entirety.

Mr Brown said: "We don't feel people driving up and down the Kingsway will feel comfortable using the road around the development and we don't feel pedestrians will be able to cross the road well enough around the site.

"One of the issues is we don't think there are enough crossing points from the Kingsway over to the development.

"There are a lot of what you may describe as minor points which make the scheme not add up and when push came to shove, we had to say no."

The advice of English Heritage and CABE is likely to hold great weight if the development goes in front of the city council's planning committee.

But the council and Karis last night played down the criticism and said they were still on course to realise the plans.