Labour's general secretary has attacked the Liberal Democrat "franchise operation".

Slamming the "contradictory" policies of Britain's third party, David Triesman said the Brent East by-election should focus minds on the nature of Charles Kennedy's troops.

Saying he would "never be complacent", Triesman claimed the Lib Dems had scammed their way to victory in the north London seat.

"Any by-election loss focuses the mind, mid-term or not," he told conference.

"I hate losing. I share the profound irritation of losing to the Lib Dems, not out of sour grapes, but because their dishonesty is so blatant."

Charles Kennedy's party would say whatever voters wanted to hear, said Triesman.

"Old fashioned left pretence in London. Outflanking traditional conservatives to the right in Somerset or Devon," he said.

"Nestling even closer to the hard right agenda in towns like Burnley."

The Lib Dems had exposed themselves as "populist, opportunist", he claimed.

The party was making progress by "shifting their argument like double-glazing salesmen".

"They will tell you anything they think you want to hear," he said.

"However contradictory their beliefs, all of them entitled to hang the name Lib Dem over their door with Charles Kennedy's approval.

"It's hard to think of them as a political party - they are more like a franchise operation.

"The outlets serve up anything from London socialism lite to Lancashire xenophobia heavy."