The controversial King Alfred development has negotiated its final planning chicane despite a last-minute attempt to derail the process.

But while developers Karis prepare to start building work next spring, the Regency Society said yesterday that it will be consulting lawyers on a judicial review.

The conservation group submitted lengthy legal advice to the council before yesterday's meeting, explaining why it believed the planning decision in March could be reviewed.

The meeting was initially scheduled for 9.45am but was delayed after the report was distributed and councillors sought legal advice.

After an hour-and-a-half of confidential discussions, Brighton and Hove City Council planners agreed to sign off the package of investment linked to the £290 million Hove seafront project.

Planning permission could not officially be granted until the section 106 money was agreed.

Three Green and Labour councillors voted to approve the conditions while Conservative members abstained.

Council leader Brian Oxley said: "As this development has already been given landlord's consent and conditional planning approval I'm anxious to see that the city gets the best possible package of benefits out of this valuable site."

A fortnight ago council officers were stripped of the power to approve the section 106, as councillors took control of the process.

Many feared the move would be used to frustrate the development and Karis and international financial backer ING threatened to sue the council for up to £60 million.

Ted Kemble, chairman of the committee, said: "The reason the report came back this week, rather than next, is because we were in a position to sign the section 106 off.

"When I was speaking in opposition to the King Alfred I was representing the views of my residents, not sitting as chairman of the planning committee.

"We had to secure the best possible conditions from the section 106."

The decision was welcomed by Josh Arghiros, managing director of Karis, who said: "We are delighted the new administration have had the opportunity to discuss it and we are looking forward to starting the building."

Michael Ray, chairman of the Regency Society Brighton and Hove, said he was disappointed the council failed to take the organisation's advice.

He said: "We thought we had given the administration a way of reversing the decision but they do not have the nerve to do it. I think they were frightened away.

"We shall now consider whether we go for a judicial review."

The legal action would challenge the lawfulness of the council's decision in March this year, taken before the local elections which saw power on the council pass from Labour to Conservatives.

Valerie Paynter, of anti-King Alfred group Save Hove, said: "They had the opportunity to go back and revisit their position with a new report but they did not have the nerve to do it."

The Frank Gehry project will lead to a new sports centre and 750 homes as well as £40 million in section 106 investment.

Building work is expected to start next year and the sports centre could be open two years later.

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