Charles Kennedy has warned the government's failure to commit to a euro referendum is hurting the "yes" camp.

In an interview with the FT on Tuesday, the Liberal Democrat leader said that Downing Street's stance is making it "very difficult to run a Yes campaign".

Kennedy also claimed that chancellor Gordon Brown's famous five economic tests had "substantially" been met but added a test of his own - that the value of sterling had to fall further. As the value of sterling had been falling since September, this too was near to being met.

"It's all there waiting to happen but it does require somebody to fire the starting pistol," Kennedy said.

"Its very hard to go out and raise support, enthusiasm and money for a campaign that isn't yet happening."

Kennedy said that until Tony Blair got behind a "yes" campaign there was little point in anyone else taking on the eurosceptics.

"The difficulty is there is no shortage of people willing to give both a public credibility as well as a financial contribution but if the government's not willing to put its head above the parapet why should they," he said.