Martin Lewis issues warning to Octopus, British Gas and EDF customers who could be owed hundreds

If you've changed your energy provider in the last five years, you could be missing out on hundreds of pounds hidden away in closed accounts as £240 million is sitting unclaimed.

According to Martin Lewis' Money Saving Expert blog, as many as two million closed energy accounts are sitting with credit in them, meaning you could be due an unexpected refund.

The industry regulator Ofgem has said that while the majority of the accounts will only be holding a few quid here and there, there are many with more than £100 sitting in, so it would be rude not to check if you fall into this category.

You're probably wondering how so many accounts have credit left in them, when refunds are usually issued automatically when you close an account under Ofgem rules.

You could be owed money if there's credit in your old energy accounts (Getty Stock Images)

Well, if you happened to be closing the account because of moving home, like so many people do, and didn't update the energy provider on your new address or contact details, they may have been unable to contact to organise the refund.

It could also be that you closed down the direct debit before the refund was able to be issued, in which case you'll need to take action.

How check if you're owed a refund and claim it back

First things first, if you still have the login for your previous energy account, you can log in and check the balance. This should tell you whether you're owed any credit and if you are, you can request it to be put back into your account. You'll just need to provide your up-to-date details.

However, if you don't know your login details then you'll need to contact your old energy supplier directly, either by phone, web chat or sending a direct message on social media.

An unexpected windfall could be coming your way (Getty Stock Images)

You should just need to provide a few details like the address on the account, your name and contact details and possibly your old account number if you can find it. If there's any credit in the account, they should be able to sort a refund for you.

If you're struggling to remember who your old provider was, try searching the names of the main energy companies into your emails to see if you can find any correspondence.

According to Money Saving Expert, you'll need to be wary about anyone contacting you claiming you're owed credit as energy companies will not be contacting people directly.