Eight supermarkets have signed up to a new set of principles from the Office of Fair Trading to address concerns over grocery special offers and promotions - but Asda is not among them.

The agreement follows an OFT investigation into supermarkets, which found they were inconsistent in how they interpreted and applied consumer protection rules.

Tesco, Sainsbury’s, Morrisons, Waitrose, Aldi, The Co-operative Group, Marks & Spencer and Lidl have agreed to adopt the principles, but Asda has yet to sign up.

“We’re supportive of the work carried out by the OFT, but we’re taking time to consider the recommendations in detail,” a spokeswoman said.

The principles include: not marketing a price as a discount for longer than the higher price was initially charged ensuring items with a ‘value’ claim on pack are always the cheapest way of buying that item in store and not artificially manipulating prices to make future discounts more attractive.

Clive Maxwell, CEO of the OFT, said: “We are pleased that supermarkets have engaged constructively throughout our investigation and we will keep a watching brief on promotions.”