A derelict patch of land smaller than a football pitch has been sold for £5.5 million.
Developer George Wimpey has snapped up the 1.5-acre site at the edge of Hove Park in Hove.
Permission already exists to build 44 two and three-bedroom homes and an office block as part of a proposed business and residential area, the £65 million City Park.
More than 1,500 people signed a petition in protest when planning permission was granted for the entire site, formerly Alliance and Leicester, to the Sussex-based Cuckfield Group in January last year.
Wimpey's part of the project includes three offices, one with a floor space of almost 80,000sq ft which will be the biggest office ever built in the city without a named prospective tenant.
Business leaders said the purchase showed big firms had faith in Brighton and Hove's continuing economic boom and about 1,800 new jobs would be created.
The presence of 21 low-cost homes elsewhere in the development is in line with the council's policy designed to tackle the chronic housing shortage.
David Huggett, managing director of George Wimpey South London, said the high price was justified.
He said: "It is a valuable piece of land in an excellent location and we see it as a good opportunity for the company."
When the project was first proposed in 2001, people living nearby said it was too ambitious. While many were pleased the dilapidated Alliance and Leicester office was to be torn down, they feared of the impact of extra traffic and homes on surrounding streets.
More than 50 people held a demonstration outside Hove Town Hall and later packed the public gallery holding placards as councillors voted in favour by a majority of seven to three.
But with the deal sealed, phase one of construction is now set to press ahead under the management of the Warings Group.
The offices are due to be completed in June 2004.
Cuckfield Group director Ronald Persaud said: "Our confidence in Brighton and Hove as a strong, vibrant commercial area is underlined by the speculative building of the first phase of this exciting scheme.
"We are delighted to be kick-starting a development that will create jobs and attract investment to the area."
The Cuckfield Group will be contributing towards improvements to Hove Park, road improvements and artistic works worth £750,000 as part of the deal.
Hove MP Ivor Caplin said: "The development as a whole has planning permission and will hopefully create employment and new homes on that site, which is to be welcomed.
"It would be useful to know what employment opportunities the developers have secured so far."
Jayne Bennett, of the Hove Park Residents' Association, said: "I haven't seen the latest plans yet but we are concerned about the impact the extra traffic will have.
"The Wimpey homes were all flats and initially we said there were too many on the site. We have got quite a few concessions though.
"We never thought we would stop development there. It was always going to go ahead but the biggest concern was traffic and parking.
"There have been a lot of road safety improvements but there is still a lot of concern.
"Everyone will watch the site carefully."
Brighton-based Stiles Harold Williams has been appointed as joint letting agents for City Park together with Knight Frank's London West End office.
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