LONDON (Reuters) - A U.S. plane carrying "dangerous goods" en route to Tel Aviv refuelled at a British airport on Saturday, a day after Washington apologised to London for breaking rules on Israel-bound flights with bombs onboard.

A second U.S. flight to Israel will also stop at Scotland's Prestwick airport on Sunday, said a spokesperson for the Civil Aviation Authority, Britain's independent aviation regulator.

Critics of Prime Minister Tony Blair's staunch support for U.S. President George W. Bush over Israel's bombardment of Lebanon expressed outrage over the new flights, saying Britain should not be used to transit bombs to Israel.

Bush apologised to Blair on Friday in the U.S. capital after Britain complained that Washington had not followed correct procedures on flying bombs to Israel via Prestwick.

"A cargo flight operated by a commercial cargo operator flew to Tel Aviv today via Prestwick and there'll be a second flight tomorrow," said the spokesperson for the aviation regulator.

"We've provided exemptions from dangerous goods regulations." He said he was unsure of the precise nature of the hazardous materials being transported.

The Foreign Office declined to comment on the flights but said Britain would grant permission for flights carrying arms defence equipment provided proper procedures were followed.

Menzies Campbell, leader of the opposition Liberal Democrats, said the new flights added insult to injury. "Who can tell if some of this equipment may be used to continue Israel's disproportionate attacks on Lebanon?" he said.

"The British government should be pursuing an active policy of denying weapons of any kind to anyone in the Middle East who may be assisting the conflict in any way."

Reports of the Israeli-bound U.S. flights have added to widespread criticism of Blair's support for Bush over the Middle East crisis and his failure to call for Israel immediately to stop its bombing campaign.

British media reported on Wednesday that aircraft carrying "bunker-busting" bombs from the United States to Israel refuelled at Prestwick. British officials have not commented on the flights in detail but do not dispute those accounts.