Money Saving Expert founder Martin Lewis returned to ITV tonight to host the Martin Lewis Money Show in which he sent a warning to pensioners.

He discussed, travel insurance, energy tariffs and debits before focusing on telling pensioners to 'not bin' a letter that is 'not a scam'.

We've all done it, looked at a piece of post and immediately discarded it, but everyone's favourite money-saving guru has warned against that. It could earn you £1000s.

Money Saving Expert explains how HMRC has started writing to 100,000s of people – mostly women – who may be missing out on their full state pension entitlement due to an error in their national insurance records. They could be owed thousands as a result, Martin explained.

Specifically, this affects those who took time off work to care for family between 1978 and 2010, as they may be missing what's known as 'home responsibilities protection' (HRP).

Letters are being sent out in phases, with those over the state pension age (66) being contacted first.

Here is what to do with the letter

What the HMRC letter will say and how to check if it's genuine

The letter will be titled "You may be eligible for Home Responsibilities Protection", and will direct you to visit the Gov.uk HRP page.

If you're worried that a letter you've received might be a scam, it's best not to act on it until you've confirmed it's authentic.

You can check a list of recent letters sent by HMRC at Gov. uk. You can also contact HMRC directly by calling 0300 200 3500 if you're still unsure.

Do note: HMRC will NEVER threaten arrest or push you to transfer money over the phone. 

If you've got the letter, check you're eligible to boost your state pension

You'll be asked to check whether you were eligible for HRP between 1978 and 2010, which you can do online on Gov.uk. If the checker says you're eligible, you'll be able to submit your claim online and HMRC will update your national insurance record, which may increase your state pension payments.

If you're unable or don't want to claim online, you can request a paper claim form by calling the national insurance helpline on 0300 200 3500.

Haven't got a letter but think you might be eligible for HRP? Hang tight for now

People currently getting the state pension are most immediately affected, as the gaps in their records could be having a direct impact on their payments right now – so that's the group HMRC is prioritising first, with those close to retirement to follow.

If you're still years off state pension age, it's best to hold off applying for the time being and wait for HMRC to contact you – otherwise, the process could slow down for everyone. In the meantime, if you've changed address, make sure you let HMRC know.

Martin Lewis Money Show returns next week on ITV 1.