Percy Pigs fans are in for a treat after a little-known way of getting free bags of the popular sweeties was revealed by a thrifty M&S shopper.

Percy Pigs are one of M&S' most popular and iconic food items with people across the country raving about how tasty they are.

But now you can get a free bag every month using a simple trick revealed by a mother who regularly shops at M&S.

She said that those shopping at the chain can get a free bag when they take part in the brand's sustainability scheme.

M&S shoppers can get free Percy Pigs and Colin the Caterpillar sweets by donating old clothes

Shoppers just need to take in their preloved clothes to the M&S Shwop bin, scan the QR code and check their Sparks app.

Those who take part will then be offered a free bag of Percy Pigs or Colin the Caterpillar sweets to thank them for their efforts.

Of the scheme, M&S said: "Every time you place pre-loved clothes in one of our Shwop boxes they're resold, reused or recycled, so absolutely nothing goes to waste."

The best part about this trick is that shoppers don't have to Shwop clothing items purchased from M&S with clothes and more from any store being eligible.

On top of this, if you Shwop in an Oxfam shop and donate an M&S item of clothing, you will be rewarded a £5 clothing and home voucher to use in-store.

The tip was shared on Instagram by the popular thrift account @thismumsavesmoney.

In a post, they told followers: "Finally I’ve made it into town and remembered to take along my decluttered unwanted item of clothing in exchange for a free bag of Percy pigs with the M&S Shwop offer.

You can do this once every 30 days!"

Fans of the account praised the tip with one user reminding customers: "Don't forget you can get the big £4 bags."

With another eagerly adding: "I’ll be taking my wardrobe there now."