The Liberal Democrats have announced plans to protect the 'triple lock' for state pensions.

But the party will strip wealthier pensioners of the winter fuel allowance, at a cost of up to £300 a year to older people.

An estimated 600,000 pensioners with annual incomes above about £45,000 would lose the allowance under the Lib Dem plans, saving the Treasury around £105m.

But the party said all of those receiving the full state pension would enjoy a rise from £122.30 to at least £137.15 a week by 2021, the equivalent of an extra £772 a year.

The manifesto plans have been welcomed by Norman Lamb, former Liberal Democrat MP and prospective parliamentary candidate for North Norfolk, the constituency with the eleventh highest number of pensioners in the country.

Mr Lamb said: 'The Liberal Democrats are making a clear commitment to older people in Norfolk, unlike the Conservatives who have repeatedly refused to give this guarantee.

'The triple lock has succeeded in lifting thousands of pensioners out of poverty, but many are still struggling to get by.'

He added: 'This commitment will ensure older people are able to meet their basic needs and that their living standards will be protected, especially with prices set to rise in the coming years.'

The triple lock was a feature of the Liberal Democrat manifesto in 2010 and a key demand in coalition negotiations. Since its introduction in 2010, it has seen pensioner incomes rise faster than average earnings, sparking warnings from the independent Institute for Fiscal Studies that it will swallow up an ever greater share of state spending.

A cross-party House of Commons select committee report earlier this year described it as 'inherently unsustainable' and recommended it should not be continued beyond 2020.

Labour has also pledged to retain the triple lock, which guarantees the state pension will rise in line with inflation, average earnings or 2.5pc, whichever is the highest.

But speculation is rife that Conservatives will ditch the guarantee, after Prime Minister Theresa May declined opportunities to confirm it would feature in her manifesto for the June 8 General Election.

A Conservative spokesman said: 'Because of the strong economy we have delivered, Theresa May and her Conservative team have increased the basic state pension by £1,250.

'The real risk to pensions comes from Jeremy Corbyn propped up in a coalition of chaos by the Lib Dems and the SNP.'

A Labour Treasury spokesman said: 'You can't trust the Liberal Democrats.

'They broke their promises and would do it again.

'Only in September their former leader Nick Clegg called for the triple lock to be dropped.

'For a party with so few MPs, they cannot agree with each other on anything, as we saw with tuition fees in the last parliament, you just cannot trust what the Lib Dems say.'