Sainsbury’s has complained to rival Tesco about certain products that it is comparing in its Price Promise coupon at till scheme.

Sainsbury’s chief executive Justin King said there are “significant challenges” in comparing own brand products as “most of our own label is not comparable”.

Sainsbury’s group commercial director Mike Coupe said the grocer had complained to Tesco about certain items which are “impossible to compare”. He said the complaint would likely lead to the Advertising Standards Authority getting involved. Retailers are required to complain directly before getting the Advertising Standards Authority involved in a dispute.

Coupe said a “significant majority” of the products are not the same.

King stressed the provenance of the ingredients that Sainsbury’s uses in its own label products. “We use high animal welfare meat, we have longstanding commitments on British products, our fish is MSC certified,” he said. “All of this means our own label is of a higher quality therefore there isn’t a fair comparison.”

Tesco launched its Price Promise, which offers vouchers at till comparing the prices of branded and own label products with Sainsbury’s, Asda and Morrisons, two weeks ago. Sainsbury’s and Asda’s price schemes compare prices just on branded products.

King said: “Our customers understand Brand Match which promises to be cheaper on branded products and believe it is the leading price promise.”

On its website, Tesco says it “can be tricky” to compare own label products. It says it only matches similar own label products, for example Tesco Finest with Sainsbury’s Taste the Difference, and takes into account things such as ingredient mix, country of origin and pack sizes.

A Tesco spokeswoman said: “It is quite a lot of work for us to do, but we use clear guidelines to ensure the comparisons are fair. And ultimately we do this because it’s what customers want us to do, given that approximately half of the average shopping basket in the UK is made up of own label products.”

Tesco’s Price Promise also compares prices on online shopping as well as in stores, while Sainsbury’s Brand Match just compares prices in stores.

Tesco UK managing director Chris Bush said in a blog last week that Tesco is the “only multichannel retailer to offer this automatic comparison to both online and store customers”. He added: “We also ensure customers can redeem coupons online and in store, regardless of where the original shop was done.”

Bush added: “Online is the fastest growing area of grocery retail in the UK, so it makes complete sense to us to include it in the Price Promise. Our customers want to know that however they choose to shop with us, we’re comparing prices and making sure they don’t lose out. As well as making sure that they can do what matters to them, using the channel they want.”

King said that while the grocer had no immediate plans to change its Brand Match scheme, in terms of offering it for online orders, it is “always looking at that side of things but for now we think in stores is the right place to do it”.

Sainsbury’s reported a strong fourth quarter, which contributed to a 1.8% rise in full year like for likes, buoyed by a surge in own-brand sales today.

Total sales in the 10 weeks to March 16 rose 6.3% excluding fuel. Full-year like-for-likes rose 1.8% excluding fuel and 1.1% excluding fuel and extensions.

Fourth-quarter like-for-likes excluding fuel rose 3.6% in stark contrast to rival Morrisons which last week reported a 4.1% plunge in fourth-quarter like-for-like sales.