A damning report into HM Revenues and Customs found that “service failures” could have led to 3.2 million people in the UK paying the wrong amount of tax in the 2014/15 tax year.

It’s a common misconception that HMRC will automatically return any tax you are due, says Tax Rebate Services, which helps taxpayers get back money they are legitimately owed.

Below is a step-by-step guide from Tax Rebate Services to reclaiming your money:

Have you received a P800 Tax Calculation from HMRC?

If HMRC has calculated that you have paid too much or too little tax, it will send you a P800 tax calculation in the post to confirm what you’re owed or what you owe.

When you receive your P800, you should check the details are correct by comparing the figures with your P60 End of Year Certificate, P11D End of Year Expenses and Benefits and any expenses you’ve claimed.

If you’ve received a P800 that tells you that you’re due a tax rebate, you’ll automatically receive a cheque within 14 days. If your P800 says you have underpaid tax, your tax code will change for the following year to allow HMRC to reclaim the tax.

If you haven’t received a P800 in recent years, you could still be owed money. At any time, you can claim all the tax you’re owed dating back four tax years. As of 2016/17, you can claim back to 2012/13.

How to work out your taxes

Using the sum of your gross pay before tax from your P60, deduct your personal allowance to find your taxable income.

The below table lists the income tax rates and personal allowance thresholds over the last few tax years:

For a quicker calculation, use a tax calculator.

How do I claim my tax refund?

1) Claim to HMRC online

The Government Gateway is an online platform that allows you to access and use local and national government e-services safely and securely. You can create an account on the government site or if you’ve used it before, log in and you’ll be able to make a claim then.

You will need your employer’s PAYE reference number, which is on your P60 End of Year Certificate, and details of any taxable income you have received, including benefits.

2) Call or write to HMRC

You can call or write to HMRC to explain why you think you’re owed a tax rebate. You will need to provide your National Insurance number and details of the jobs you’ve had and any state benefits you’ve received over the period of time you’re claiming for.

3) Use a Tax Rebate Service

If you have never claimed tax before and are unsure on what you may be entitled to, or simply don’t have time to fill out the paperwork yourself, you could use a third party service that claims back tax on your behalf, such as Tax Rebate Services, though this works on a no win no fee basis, so bear in mind that if you are owed any tax, you’ll receive less than the full amount once the service charges have been added.

What happens next?

Once you’ve made the claim, you’ll usually receive a payment in the form of a cheque within 12 weeks.

Could you reclaim other work-related expenses?

1) Mileage Allowance relief

If you use your car to travel for work, and your employer doesn’t reimburse you the full allowable mileage allowance, you can reclaim a flat rate per mile. Separately you can also claim back public transport tickets, congestion charges and parking fees.

2) Uniforms Tax Relief

If you clean a company or specialist clothing for work, it’s eligible for tax relief going back up to four years. It’s useful to keep receipts for purchases and laundering costs, but you can receive a flat rate reduction for washing at home, which doesn’t require receipts.

3) Tools Tax Relief

If you need to buy tools or equipment in order to do your job, and you haven’t already been reimbursed by your employer, you could claim back up to 18% of their cost. You will need proof of purchase to make a successful claim.