Martin Lewis' Money Saving Expert has issued a warning to millions of Tesco Clubcard holders to spend 50p by this Friday. The financial advice website is urging shoppers to double check their voucher expiration dates as they only have "days left."

On the MSE website, it advised: "If you've got a Tesco Clubcard, check when your vouchers are due to expire as you've only days left to spend or extend nearly £17 million-worth before they run out on Friday 31 May."

Furthermore, over £27 million in 'Reward Partner' codes vouchers that have been exchanged to spend at various third party retailers are set to expire within the next fortnight.

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If you don't wish to spend your Clubcard vouchers, you can attempt to extend them, according to MSE.

The site advised: "Technically, under the Clubcard TandCs, Tesco can refuse a Reward Partner order if it decides you're trying to game the system by redeeming vouchers just to extend their validity but we tested the trick at MSE Towers this month and it worked just fine.

"If you want to give this a try, here's how it works though remember you'll need to extend your vouchers by 11.59pm on Friday 31 May."

To do so, make a small purchase on the Tesco Clubcard Rewards page (not in store or on other Tesco pages) or donate to one of its partnered charities, MSE suggested.

"The remaining balance is credited back to your Clubcard account as points. So if you spend 50p using a £5 Clubcard voucher, you'll get 450 points back (worth £4.50). You can then swap your points for vouchers manually or wait for them to be converted with your next statement.

"There's no minimum spend, but the aim's to shell out as little as possible."

It notes: "A good option might be a 50p restaurant voucher."

More than 100 reward partners are available, such as Cineworld, Chessington World of Adventures, Thorpe Park and Zizzi.