Asda has accused WHSmith of  “rip-off” stationery prices as the battle for back-to-school sales heats up.

After comparing prices on a basket of 20 stationery products such as pens and pencils, Asda claimed to be more than 50% cheaper than WHSmith.

The grocer accused the bookseller and stationer of charging “outrageous” prices and alleged: “WHSmith stationery prices are too stationary – they need to come down.”

Asda said it had made a like-for-like comparison and flagged differences such as a 50p flexible ruler, which cost 50p in its shops but £2.19 at WHSmith.

But a WHSmith spokeswoman countered: “Based on our analysis we believe the product and price comparisons stated by Asda are simply not comparable. 

“WHSmith prices stated are not current in-store promotional prices and there is a distinct differentiation in quality across all products, with WHSmith products being of superior quality.”

Asda ‘stationery expert’ David Walker said: “If the cost of buying a basket of essentials from the UK’s most famous stationers is double the price you’d pay at Asda, it’s very important shoppers know that.

“It’s easy to spend upwards of £30 on back-to-school stationery even at Asda prices. The idea that it would cost you more than £60 for the same at WHSmith makes no sense at all.”