The WPP-owned RKCR/Y&R handles M&S’s advertising account but Campaign has learned that other shops within the network – including Grey London and Ogilvy & Mather – had been asked to put forward ideas.
A spokesman for M&S told Campaign: "Rainey Kelly is our creative agency partner and we have no plans to review this."
In the three months to 27 December 2014, sales in clothing and homeware at M&S dropped 5.8 per cent, while food sales increased by only 0.1 per cent. The declines were attributed to distribution problems, mild weather and aggressive discounting by its rivals.
However, M&S’s fortunes have since improved. It posted a 0.7 per cent rise in clothing and homeware in the first three months of this year.