Marks and Spencer is planning to extend its experiment of selling branded products, including Tetley tea and Hellman’s mayonnaise, to 20 stores across south-east England.

The retailer, which last year broke with 85 years of tradition when it began stocking up to 350 big-name brands in 19 stores dotted around Tyneside, will begin its trial in the south towards the end of April, according to suppliers.