Peter Harrison, chairman and backer of Britain's America's Cup team, will pull the plug on the GBR Challenge unless another sponsor willing to invest up to £30 million is found by the end of August.

GBR Challenge have five prospective backers for the 2007 event in Valencia with whom they have been in talks since the of end of last year. Representatives of some of them will come to Skandia Cowes Week next week for talks.

But if deals are not signed, Harrison is unlikely to carry on. He spent around £22 million on the first challenge in 2003 and another £3 million in Britain on funding research, tank testing, renting a temporary base in Valencia and maintaining a small core team.

Harrison, who has funded ongoing operations since returning from Auckland in March 2003, said: "The decision can't be far away. We only have another month."

Harrison, who returned Britain to the America's Cup for the first time since 1987, has made a very attractive pledge for the 2007 event. He will put in £20 million if commercial partners can be found to put in a further £20-30 million to make up the balance for the the £40-50 million budget needed.

In recent weeks GBR 70 has returned to sailing in the Solent under Adrian Stead.

Several overseas sailors have visited the British set-up, including Ed Baird, skipper of Young America in the 2000 Cup. He had been in talks about the possible team leader/skipper role. Cameron Appleton, one of Dean Barker's Team New Zealand tune-up helmsman, has been sailing on GBR 70.