Want to bag a bargain at Costco but don’t think you’re eligible for membership? According to Martin Lewis, you might be.

In the latest edition of his newsletter, the Money Saving Expert (MSE) founder shared a ‘secret’ way of joining the club, which offers its members and their partners lower prices for buying in bulk.

There are 29 Costco warehouses around the UK, with discounts on everything from toiletries and groceries to petrol and big-ticket tech.

You can’t just walk in and start shopping though, and only certain professions can apply for in-store membership (priced from £26.40 a year).

Alongside business owners, qualifying roles include the likes of local government, banking, medicine, education or the police.

But even if you don’t fall into one of these categories, you may still be able to get in on the savings.

How else can you join Costco?

Revealing a ‘little-known’ avenue, MSE explained: ‘AA, RAC and National Trust members are eligible to join at certain locations.’

Where can AA, RAC, and National Trust members shop at Costco?

As the retailer doesn’t advertise these memberships, the financial gurus called every UK Costco to check if the rumours were true. And, while it doesn’t seem to be a countrywide option, they were told it worked at Birmingham, Sheffield and Cardiff.

There is one catch: you can only shop at the location you joined at. Martin also recommends calling before making your first trip, just in case the rules have changed at your preferred warehouse.

Once you get the go ahead however, it’s as simple as rocking up to the membership counter with the relevant ID and using your coveted Costco card to shop ’til you drop.

That said, MSE has some advice to help you make the most of your experience, as it can be a little overwhelming for a first-timer.

The experts claim taking a shopping list and sticking to it is ‘the number one rule’ at Costco.

Otherwise, the huge range of products and lack of signage could mean ‘you’ll pop in for bog roll and come out with a canoe, a 6ft teddy bear and a crate of 30 Danish pastries.’

Next, they advise a dose of skepticism, saying: ‘Just because something graces Costco’s shelves, it doesn’t automatically make it a good deal. Always do your own research first and check if you can get it cheaper elsewhere.’

Compare unit prices (since Costco sizes are normally different) and consider downloading the Trolley.co.uk app to compare on the go.

Although Costco is often cheaper when it comes to branded goods, you may find supermarket own-brands or the likes of Aldi and Lidl come out cheaper.