Passed by a majority of at least two to one, the boycott motion is likely to be as painful for the party's wine-loving middle class membership as for the French.
Paddy Ashdown, the party leader, and other senior figures were understood not to favour the ban but no attempt was made to thwart it. Mr Ashdown has a cottage in Burgundy which, if he obeyed the boycott to the letter, he would be unable to visit.
Matthew Taylor, MP for Truro, acknowledged the power of a consumer boycott in persuading Shell not to dump the Brent Spar oil rig at sea but said it was more important to put pressure on John Major over testing. "We should encourage voters to write to the Prime Minister and let him know that if he stays silent they will boycott the Conservatives come the election."
Picking on a report that Britain gets data from the Mururoa explosions, Mr Taylor said that if Mr Major continues in his "disgraceful complicity" with the French, he will share responsibility for a Pacific Ocean which will be radioactive for thousands of years.
The Truro MP moved a motion calling for an end to the tests and deploring Mr Major's refusal to condemn them. But the boycott was added in an amendment passed to loud cheers. For some Liberal Democrats the instruction is unnecessary. Wine lists, cheese boards and menus had already come under scrutiny in Glasgow this week by delegates keen to mark abhorrence of the tests.
Recommending Bulls Blood and Soave, Graham Watson, MEP for Somerset, said the personal acts of hundreds of thousands of individuals could influence multi-nationals and governments.
Elizabeth Shields, former MP for Ryedale, said they should "hit hard at the French economy", while Brian Moore, a Newcastle city councillor, said Jacques Chirac had "dealt a slap in the face" to negotiations to halt the spread of nuclear weapons. "The French president has seen fit to ignore the evidence of exports around the world. He has seen fit to ignore the protests of political leaders around the world. So now it's up to us," he said.
Liberal Democrats in Newcastle upon Tyne are opposing a pounds 600m takeover bid for Northumbrian Water by the French company Lyonnais des Eaux in protest at the tests.
But Sue Vincent, of Reigate, thought a boycott was an impossible task. "When you turn on your taps or lights, you are probably using a partially French-owned utility," she said. Steve Melia, of Totnes, worried about being accused of causing lay-offs in British plants making Peugeot cars.
Not on the platform for the debate, Menzies Campbell, the party's defence spokesman, had repeated the party's opposition to the French tests earlier in the afternoon. "For any country to embark upon a series of nuclear tests immediately after signing an extension of the Nuclear Non-Proliferation Treaty cannot be justified," he said.
Mr Campbell said both France and China should bring an end to their nuclear tests immediately. He also wanted the cause of multilateral nuclear disarmament made a central part of British foreign policy - "not something to which we pay occasional lip service".