David Cameron is one of the "most dangerous Prime Ministers" in living memory and the administration he runs "has all the makings of one of the worst Governments of our time," Paddy Ashdown has said.

The former Liberal Democrat leader said Mr Cameron was a "decent man with broadly decent instincts" but said that in the space of "just 70 days" he had unintentionally put the future of the UK in jeopardy.

He had done so through his plans to hold an in-out referendum on the EU, his proposals to exclude Scottish MPs from English-only laws and accused him of putting a "noose around the neck of the BBC". "He does it all unwittingly," he said. "But that does not lessen the damage."

Unlike Charles Kennedy, his successor as Lib Dem leader, Lord Ashdown was supportive of the party entering into coalition with the Conservatives in 2010 and was consulted on the decision. But giving answers in a Q&A on the Reddit website, Lord Ashdown was scathing of his party's former coalition partner.

"I really believe this has all the makings of one of the worst Governments of our time," he said. "I think Mr Cameron is one of the most dangerous Prime Minsters I can remember.

"He does it all unwittingly. But that does not lessen the damage. He is so short term, casual and unthinking about the things he grabs hold of.

"And the consequences? In 70 days (just 70 days) he has put the Union at risk, ditto our future in Europe, placed a charge of dynamite under our constitution with EVOL and put a noose around the neck of the BBC. Not bad considering all has been done by accident."