LONDON, United Kingdom — Marks & Spencer Group Plc said on Saturday its chief financial officer, Humphrey Singer, was stepping down after little more than a year, a further setback as the retailer is demoted from Britain's leading share index.

Singer, who joined from electricals retailer Dixons Carphone in 2018, will work with Chief Executive Steve Rowe on the succession process, the company said.

Marks & Spencer, a 135-year-old firm that is one of the biggest names in British retail, has struggled to compete effectively on clothing with the likes of Zara and H&M, and will be relegated from London's FTSE 100 index of leading shares with effect from Sept. 23 because of its declining market valuation.

It has built up a well-regarded food business that seeks to combine convenience and indulgence.

This now accounts for more than half of its annual revenue but margins have come under pressure from the march of discount chains, and M&S has reported three straight drops in annual profits..

"After eighteen months of working with Steve to lead the transformation strategy and rebuild the finance function, I have decided that now is the right time to move on," Singer was quoted as saying in a company statement.

Singer's exact departure date has not yet been decided and he will continue with his responsibilities until it is confirmed, the retailer said.

"Humphrey has been a huge asset to the business ... I look forward to continuing to work with him as we search for his successor," chief executive Rowe said.

Singer's abrupt departure follows the sacking of clothing, home and beauty managing director Jill McDonald in July, after which CEO Rowe took direct control of the division.

In its latest turnaround plan, M&S has been closing weaker stores, revamping ranges and investing in online sales.

Its boldest move yet was striking a £1.5 billion joint venture with online grocer Ocado to give M&S a home delivery service for food.

By Bhargav Acharya and Sabahatjahan Contractor in Bengaluru; Editors: Keith Weir and Kevin Liffey