A watchdog has upheld complaints about an advertisement for building a giant out-of-town car park.

The Advertising Standards Authority (ASA) ruled Brighton and Hove Business Forum exaggerated the benefits a 1,000-space commuter park-and-ride site would have on the city.

The forum produced an advert that stated: "Congestion is killing the city - park-and-ride with 1,000 spaces will reduce vehicle movements by 700,000 per year and will reduce carbon emissions by 330 tonnes per year."

The figures were challenged by Brighton, Hove and Mid-Sussex Friends of the Earth; the Sussex, Brighton and East Grinstead RSPCA and five members of the public.

The forum said that after receiving the complaint, it reviewed its figures and realised it had miscalculated the results of a 1,000-space car park.

Executive director Tony Mernagh said: "It was an oversight, which I hold my hands up to and apologise.

"There was no intention to deceive."

The advert was placed in The Argus last November to support the business forum's case for a park-and-ride site at Braypool, which was rejected by Brighton and Hove City Council along with an alternative at Patcham Court Farm.

Chris Todd, from Friends of the Earth, said: "The business forum has been caught out with its wild claims about park-and-ride and we hope that in the future, people will be more sceptical about its use of such statistics.

"We have always said that these figures were complete hogwash."

The forum's calculation was based on a 1988 traffic report by WS Atkins.

Mr Mernagh said: "I based the figure on the assumption that 100 per cent of the traffic using the park-and-ride site would have previously driven into the city centre but that was a mistake. In fact, the report said only 68 per cent would. It was an oversight.

"It does not undermine the case for park-and-ride because that still amounts to half a million less vehicle movements."

However, Mr Todd said: "Research has consistently shown that park-and-ride has a large number of detrimental impacts on the environment.

"Contrary to many people's belief, it is not the green form of transport it is often paraded as being.

"In fact, rather than reducing carbon emissions as claimed by the business forum, park-and-ride could actually increase them."

He said the judgement proved the council was right to reject a park-and-ride site at either Patcham Court Farm or Braypool.

The Braypool plans were opposed by a nearby RSPCA dog walking centre, while the Patcham Court Farm scheme proposed demolishing cottages and allotments.

Frances Lindsay-Hills, from the RSPCA, said: "It's disgraceful an organisation that supposedly stands for business ethics can manipulate figures like this.

"If it was a mistake, the forum has a duty of care as representatives of the business community and this will damage its reputation."

In a statement, the ASA said: "We concluded the ad was misleading and advised Brighton and Hove Business Forum to seek advice from the Committee of Advertising Practice's copy advice team before advertising in future."

Mr Mernagh said the advert had been taken out of circulation but he would be publishing new material, taking into account the 68 per cent figure.