Ainslie's decision is a blow to British hopes

He told the Guardian he made the switch after the backers of a proposed British bid to enter the competition appeared to reach a standstill in development.

"I was approached by GBR Challenge but nothing much looked to be happening," said the Olympic champion, tipped for gold at Athens in the Finn class.

"I want to sail for Britain in future but it doesn't look good right now."

Ainslie had an aborted America's Cup spell with American syndicate OneWorld before leaving after a lack of opportunites as a helmsman to pursue his Olympic Finn campaign.

He insisted his decision to join the New Zealand team was down to personal ambition rather than financial gain.

"I want to try to be successful in the America's Cup, and this is a good opportunity," he said. "I have assurances that I will be doing what I want to do."

The boat will be skippered by Dean Barker - who will be one of Ainslie's main rivals in the Finn class at Athens.

Ainslie's decision to join Team New Zealand is another blow to hopes of a British bid, after his fellow Olympian Iain Percy agreed to join an Italian campaign.

Team New Zealand won the trophy from America in 1995 and defended it five years later, but last year lost 5-0 to Swiss team Alinghi, who had poached several leading Kiwis including then-skipper Russell Coutts.

The New Zealand team, who say they need �50m in sponsorship, hope to have their yacht in the water early next year, with the competition taking place off the coast of Spain, near Valencia, in 2007.