The online form that could net a million couples £900

 More than a million married couples are missing out on tax breaks worth up to £900, according to an analysis of official figures.

Three million others have taken advantage of the Marriage Allowance by filling out an online form which takes just minutes, HMRC says. The tax break is worth £238 a year, but those eligible customers can also receive backdated claims of up to £662 as a lump sum.

People have a tax-free personal allowance of £11,850, on which no tax is due on income up to this amount. With the Marriage Allowance, a spouse or civil partner who is a nontaxpayer can transfer £1,190 of their tax-free personal allowance to their partner – reducing their tax bill.