The longstanding policy - first touted in 1992 - has been scrapped by leader Sir Ed Davey during the party's conference, as he argued it was "unsustainable" and would be unfair to struggling households.

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The move comes the day after the Lib Dems signed off the first draft of their manifesto at their annual gathering in Bournemouth, kicking off their general election campaign with a big focus on taking Tory seats.

But it also came after one of the party's former leaders, Sir Vince Cable, appealed for more honesty over the need for tax rises to improve services.

Speaking at a conference fringe event, he said: "If we are actually going to do things with public investment and public spending, which you have to do if you are a progressive cause, this dreaded word tax is going to arise.

"The opposition parties are absolutely falling over backwards not to talk about it - just like Europe, it has become one of these unmentionable subjects.

"But if government is going to have some freedom of manoeuvre and if they actually mean what they say about fairness then taxation for additional public spending, for redistribution, is going to have to be at the heart of it. But are you hearing anybody talking about it?

"I think we have a responsibility actually to get that kind of conversation started, with Labour people and indeed ourselves."

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Speaking to the BBC, Sir Ed did not deny the need for more funds to improve public services - especially as the key pledges coming out of the conference are around tackling the crisis in the NHS.

But he said the cash should come from companies making "huge profits", rather than the wider public who are already struggling with the cost of living.

In an article for The Times, the leader added: "We've had two years of frozen income tax allowances and four more years to come. Those six years of stealth income tax rises equate to more than a 3p rise in the basic rate of tax.

"You can't ask working families to pay more in tax. You just can't."