The Liberal Democrats have distanced themselves from the Conservatives by warning they would not support plans to cut public spending too early in the next parliament.

The party's leader, Nick Clegg, said early deep cuts would be "economic masochism". It came as the Lib Dem treasury spokesman, Vince Cable, hit out at the Tories' economic plans. In his speech at the party's spring conference in Birmingham, Cable accused the Conservatives of engaging in a "phoney war over cuts" that would affect millions of lives. He also hit out at George Osborne, the shadow chancellor.

Cable said the Tories were trying to present their economic team as "'Slasher' Osborne and the Hard Men". But, he added, they appeared to have taken cuts straight after the election off the table – at least for now. "Or at least that's what I think they said. I'd love to attempt a critique of the Tories' budget plans, but I have no idea what they are. I think the present line on the budget is: 'Trust us and we'll tell you after the election'," he told cheering delegates.

He added: "People are desperate to see the back of this Labour government. But they don't want the same old Tories. And make no mistake they are exactly the same."

He also claimed that David Cameron's party and its "cronies" were trying to create financial panic to frighten people into voting for them. "Playing fast and loose with the financial stability of this country for political gain – destabilising the markets – is dangerous, irresponsible and wrong," said Cable.

He did not limit his criticism to the Conservatives. Cable, having famously compared Gordon Brown to Mr Bean, this time made delegates laugh when he said the prime minister sounded like the Chelsea footballer Ashley Cole, pleading: "Give me another chance."

The Lib Dems had identified £15bn worth of reductions in public spending that would cut the deficit, he said. The party has come under an increasing level of scrutiny as the polls narrow. Observers are watching for any signs to suggest whether the Lib Dems would be prepared to make a pact with Labour or the Conservatives in the event of a hung parliament. That is the scenario suggested by two polls released today.

YouGov research for the Sunday Times finds that the Tories' lead has narrowed from five points to four over the past week. An ICM poll for the Sunday Telegraph places Cameron's party seven points ahead – not enough for a majority. The same research suggests that the Lib Dems have strengthened their position and are now on 21 points.

Clegg will discuss a hung parliament when he addresses MPs today. "People often ask me what the Liberal Democrats will do after the general election. Some days I read we're planning a deal with Labour, some days that we're planning a deal with the Conservatives, other days that we'll refuse to talk to anyone at all," he is reported as planning to say.