Patrons of the burger restaurant are rushing to make use of a little-known receipt-based method that can bag them a whole meal for just £2.99.

A parent shared the savvy technique on social platforms, demonstrating how one simple step after ordering can reveal a heavily discounted rate on a second meal.

The secret involves something most diners throw away without a second thought — their receipt — which could actually open doors to considerable savings.

Once you know what to look for, it is an easy way to cut the price of your next visit to the eatery.

Diners simply need to make any purchase first, then input the code printed on their receipt to unlock a follow-up offer, according to creatorzine.com.

Shoppers are sent to complete a short internet survey using the code, and once finished, they receive a voucher to use at the restaurant.

Scanning it at the till enables them to get a Big Mac and fries for only £2.99.

The tip was shared by Gemma Bird, who operates under the username Money Mum online.

The trick has quickly spread across social platforms, with many people saying they had no clue such an offer existed.

One person expressed surprise at discovering the offer and mentioned they would be keeping their receipt for their next visit.

Another individual said they could not believe they had never known about this.

A third person called the trick fantastic.

One individual described going around to all the machines, collecting all the receipts and completing the process.

However, one user pointed out a possible problem, noting that the machines often have no receipt paper available.

The method functions as part of McDonald’s ongoing customer feedback programme, where receipts regularly contain survey codes that grant discounted meals upon completion.