LABOUR leader Ed Miliband today insisted that his party was the ''only alternative'' to the coalition Government as he joined his by-election campaigners in Eastleigh.

The opposition supremo was joined by about 50 supporters waving placards as he promoted his plans for a ''mansion tax'' and to introduce a 10p tax rate.

He also gave his backing to his by-election candidate, best-selling author and satirist John O'Farrell.

The Hampshire town is the focus of a fierce battle between the main parties, with the Lib Dems keen to prevent their Tory coalition partners snatching the seat.

Labour is hoping for a good showing in the vote on February 28, which became vacant with the resignation in disgrace of ex-cabinet minister Chris Huhne after he admitted dodging a speeding penalty.

After taking in visits to Leigh Park and the Artisan Cafe, Mr Miliband spoke of his announcement that Labour favoured reviving the 10p income tax rate.

Labour says that could be paid for by a levy on two million-plus homes - a policy promised in the last Liberal Democrat manifesto but opposed by the Conservatives.

The party hopes to put the ''mansion tax'' proposals to a vote either before the Budget in an opposition day debate or through an amendment to the Budget-implementing Finance Bill.

He said: ''This is a living standards by-election, that's the issue on the minds of so many people in Eastleigh - not being able to afford the weekly food bill, not being able to afford to fill up the car.''

He said that the Government was in favour of a tax cut for those earning more than £1 million.

''If you want that you can vote for the Lib Dems or Tories, if you want an alternative you can vote for Labour,'' Mr Miliband said. He also questioned whether Nick Clegg's party would continue their previous support for a mansion tax.

''They claim to be in favour of a mansion tax as they used to be against tuition fees, and they broke that promise.

''Is he (Clegg) going to vote with Labour to force George Osborne to do it in the budget or is he going to do what he has done for two and a half years and prop up a failing Conservative Government?''

He added: ''People can vote for Conservative or Liberal Democrat and they know they will have a Member of Parliament supporting the Conservative Government or they can vote for an alternative.''

After speaking to supporters, Mr Miliband and Mr O'Farrell had a coffee with former Huhne voters who were now considering voting for Labour at the by-election.

Tory backbenchers have been campaigning for the 10p rate to be reintroduced in next month's Budget, and the Prime Minister hinted earlier in the week that he was ready to agree with them.

Speaking before his visit to Eastleigh, Mr Miliband said: ''There could be a majority in the House of Commons when it votes on our proposal. But only if the Liberal Democrats vote with Labour.

''Now the Lib Dems say they are in favour of a mansion tax. Well, they once said they were in favour of abolishing tuition fees too.

''Here is a chance for Nick Clegg to prove he can keep at least one of his promises.''

He added: ''The squeezed middle has never been so squeezed. And if we carry on as we are it will be like that for years and years.

''All this Government has to offer is tax cuts for the richest at the top, an unrelenting squeeze on the middle, and a race to the bottom.

''That is not how we will build a successful economy again. It's time for a new approach. And that's what the One Nation Labour Party under my leadership will offer.''

He continued: ''The people of Eastleigh deserve an MP who understands that, who is on their side. His name is John O'Farrell.''

Prime Minister David Cameron and Mr Clegg have already made their first forays to Eastleigh - underlining how high the stakes are for both leaders.

A win for the Conservatives would help to convince restive Tory backbenchers that Mr Cameron still has a chance of leading them to outright victory at the next general election.

Equally Mr Clegg needs the Lib Dems to hold the seat if he is to reassure supporters that they are not facing a catastrophic collapse the next time the country goes to the polls.