Conservative spending plans will lead to the "wilful destruction" of public services, Danny Alexander has claimed in the latest public coalition spat.

Pledges to cut taxes after the general election do not add up and the party is playing "fast and loose" with the economy, the Chief Secretary to the Treasury said.

The governing parties have been openly engaged in tit-for-tat sniping since the Autumn Statement as they seek to offer voters distinct pitches in the run-up to the May poll.

In an interview with The Independent, Mr Alexander accused Chancellor George Osborne of planning £60 billion of unnecessary cuts by 2020 in an attempt to "shrink the state".

He said: "The Tory agenda to keep reducing public spending beyond what is necessary would result in the wilful destruction of important parts of our public services. That is not appropriate or right for this country.

"People are prepared to go along with deficit reduction when they see it is necessary. When you are past that point, to where it is an ideological choice, people don't agree with that."

He added: "I find it very difficult to see how you find £12 billion of savings focusing purely on working-age benefits. Having looked at it hard, I just don't see how that is possible whilst maintaining a degree of fairness and a proper safety net.

Mr Osborne's Treasury deputy said the Tories would have to make deeper cuts to meet plans for £7.2 billion of tax cuts.

He said: "The Tories are playing fast and loose with the economy and frankly with their own credibility. It is not affordable or achievable, especially as they said they do not want any tax rises. Presumably to shrink the state, they would also have to make further spending cuts needed to pay for their tax cuts. I don't think it adds up."

Labour earlier this month accused Mr Alexander of being ''thick as thieves'' with the Conservatives - despite ''pretend'' attempts to distance himself from his ''consistent record of Tory collaboration''.

Mr Alexander told The Independent his relationship with Mr Osborne is "absolutely fine".

He added: "George and I have worked effectively together in the Treasury to get on with the job of sorting out the economy.

"That is what both of us came into the Treasury to do, whilst recognising and understanding there are big political differences that cause arguments about policy."