Nick Clegg has dismissed Ukip as a party offering "a better yesterday" and said its supporters don't like the modern world.
The Deputy Prime Minister laid into Nigel Farage's party, which has regularly outpolled the Lib Dems in surveys of voter preferences over the past few years.
Asked about the surge in support for Nigel Farage's UK Independence Party, Clegg said: "I think Ukip appeals to a constituency which I totally understand.
"In a sense they are people who don't like a lot of what they see in the modern world, from what they see on the telly to how people behave to touchstone issues like immigration.
"In a sense what Ukip and Nigel Farage are projecting is a promise of going backwards... to a sepia-tinted world where there were none of these challenges. It obviously appeals to some people."
He added: "I think they appeal - and appeal strongly - to people who want a better yesterday, and I want a better tomorrow. That's the difference."
Farage said that Clegg's support for EU membership showed he was "not just dreaming of the past but living in it".
"His ideas, and the ideas of the European political elite that he so well represents, are those of the 1950s and 60s, whereas Britain must be looking for global opportunities to be fit for the next 50 years."
In the first of a series of monthly press conferences, Clegg also attacked the "loopy" proposals put forward by Tory right-wingers including banning the burkha and naming a bank holiday after Margaret Thatcher.