New figures by The Adjudicator's Office reveal that HMRC has had to issue close to £1 million in refunds and write-offs after mistakes last year. 

The taxman had to back down from demands worth £806,755 in 2015/16 after cases were referred to the independent tax dispute service.

It also had to fork out £42,485 to taxpayers for causing ‘worry and distress’ after wrongly chasing them for underpaid tax or overpaid benefits. An additional £40,095 was paid out for poor complaint handling.

The adjudicator upheld a whopping three in four complaints in 2015-16, taking the side of the taxpayer in 666 out of 914 cases.

HMRC says that there are 40 million people in PAYE and that a small number complain about its service. But if HMRC is in the wrong, it's vital that you make a complaint. Here's how to do it.

How to make a complaint

Should you feel unhappy about the way HMRC has treated you, perhaps because they are targeting you for a supposed underpayment, then don’t just accept it - complain!

You’ll need to contact the complaints manager at the relevant tax office, providing details such as your National Insurance number and the last reference number the taxman used when contacting you. You will need to detail not just what you believe the taxman has done wrong, but also what they should do to put it right.

HMRC should then respond within 15 days.

Alternatively, you can ask someone else to complain on your behalf like a friend, relative or professional adviser. Voluntary organisations like the Citizens Advice Bureau, TaxAid and Tax Help for Older People can help you out too. 

HMRC’s website has more on appointing someone to deal with HMRC on your behalf.

If you aren’t happy with the response you get, you can then ask for a senior officer (who has not previously been involved) to take a fresh look and make a final judgement.

[Read more: 800,000 overtaxed on pensions – here's how to reclaim]

Independent decisions

If you’re still unhappy, then it’s time to turn to the Adjudicator’s free complaints service.

Head over to the Adjudicator’s website, where there are full details on how to raise your case with them. Your case will only be dealt with if you’ve already complained to HMRC.

Your final port of call is the Parliamentary and Health Service Ombudsman which is free, but you'll need to ask an MP to refer you. It’s also independent and will look into the complaints after they’ve been considered by the Adjudicator.