More than 3.5m couples are already benefitting from the relief, which was introduced in April 2015, but HMRC estimates around 700,000 couples are still eligible for the free tax break worth up to £238 this year. If their claim is backdated, they could receive a lump-sum of up to £900.

Mel Stride, financial secretary to the Treasury, said: ‘Married couples who are yet to sign up for this great scheme – you too can benefit – it is quick to register and any back-dated allowances will be paid as a lump-sum.’

Marriage allowance lets lower income workers transfer £1,190 of their personal allowance to their husband, wife or civil partner, if their income is higher. This reduces their tax by up to £238 for 2018/19 tax year.

The personal tax allowance is increasing to £12,500 in April 2019. The increase in non-taxable earnings means eligible couples will be able to transfer up to £1,250 from the lower income to the higher income earner, reducing their tax by up to £250 a year.

To benefit taxpayers need to be married or in a civil partnership; to not pay income tax or have an income below their personal allowance; and to have a partner who pays income tax at the basic rate. Marriage Allowance is available in Scotland although the higher earning partner must pay the starter, basic or intermediate rate.

There is no need to reapply for marriage allowance every year because it is automatically renewed. However, couples should notify HMRC if their circumstances change and they want to cancel it.

Marriage Allowance information is here.

Report by Pat Sweet