Martin Lewis has highlighted Marriage Tax Allowance, a scheme intended to encourage marriage by offering an annual tax break. Despite being designed to benefit couples, around two million eligible couples haven't taken advantage of it.

It allows eligible couples can increase their tax-free income by £1,260, resulting in them keeping an additional £252 that would have been paid as tax otherwise. If you've been entitled to this allowance but haven't claimed it, you're allowed to backdate your claim for up to four years, potentially leading to a sizeable reimbursement of up to £1,006.

Qualifying for the Marriage Tax Allowance does have some conditions beyond a marriage or civil partnership. One partner must be a non-taxpayer meaning they earn less than the personal allowance each year, which is £12,570 annually for most.

Martin explained on his ITV Money Show: "People say 'What about if I'm volunteering? What about if I'm part-time?'... If you don't pay income tax, you're a non-taxpayer." The other half of the couple must be on the basic income tax rate of 20%, indicating their taxable income falls between £12,571 and £50,270.

To claim the Marriage Tax Allowance, the non-taxpayer partner can visit to apply to transfer 10% of their personal allowance to their tax-paying spouse. This amounts to roughly £1,260.

The non-taxpayer can then earn up to £11,310 before they are liable for income tax. On the other hand, the tax-paying partner's income tax threshold increases to £13,830.

This effectively saves the household an additional £252 annually that would have otherwise been paid to . Martin emphasised: "You can claim back up to four tax years as long as you are eligible."

He also pointed out that it must be the non-taxpayer who applies for the tax break, stating: "Clearly, you can't apply to take someone's personal allowance."