Nearly 3 million eligible couples are still not claiming the Marriage Allowance, despite a study exposing its lack of take-up three months ago and Labour branding it an "utter flop" over low figures almost a year ago.
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Set up by Tory ex-Chancellor George Osborne, the tax break lets a husband or wife hand £1,100 of their tax-free personal allowance to their spouse.
The current allowance is £11,000, so shifting it means a higher-earning spouse can earn £12,100 before paying income tax.
This benefits couples where one spouse is the only breadwinner, or the lowest-earning partner is paid less than £11,000 a year.
These couples can claim up to £220 this tax year - and another £212 if claims are backdated to April 2015, when the policy launched.
Ruth Owen, Director General of personal tax at HMRC, said: "An extra £432 is a really helpful way to start 2017, especially after Christmas."
In February last year Labour MP Jonathan Ashworth described the flagship policy as "a complete and utter flop" because of its poor take-up.
He also called the policy "perverse and unfair", saying: "It's a benefit that doesn't go to the vast majority of families, doesn't go to widows and doesn't go to people who have been left by an abusive husband."
Last February figures showed just 330,000 couples had successfully claimed.
The number has crept up since, but in October the MoneySavingExpert website found 3.2million eligible people still had to launch their claim.
In a press release on Friday, HMRC said "more than 1.3million" couples out of 4.2million who were eligible had claimed the allowance.
This appears to leave just under 2.9million eligible couples who have still not claimed the perk.
To qualify, one of you must be a non-taxpayer and the other one of you must be a basic-rate taxpayer (earning up to £43,000 a year).
Civil partners have the same rights as married couples to claim the allowance.
Married? How to claim your tax allowance
To benefit as a couple, you need to earn less than your partner and have an income of £11,000 or less.
To make a claim for your tax allowance, you must apply online via HMRC here .