A bitter war of words erupted between Marks & Spencer and the GMB after it emerged that the worker who blew the whistle on the group’s new redundancy terms will hold a press conference tomorrow.

The GMB confirmed that it plans to unveil the employee, sacked this week for revealing the new redundancy proposals to The Times, at the Trades Union Congress (TUC) in Brighton.

It will also launch a new campaign that accuses M&S of “snooping” on its workforce. The move sparked a furious reaction from M&S, which insisted it had no other choice but to sack the employee for deliberately leaking company information and making derogatory comments about the business.

In a statement the retailer said: “We are astonished by the actions and allegations the GMB has made about the dismissal of one of our employees.

“Despite claims that they plan to appeal on behalf of the individual, the GMB seems more concerned about conducting the case through the media to gain publicity for their own ends.”

M&S added that it had not been listening in to its staff, but had simply identified the employee through e-mails he sent to The Times during working hours.

Sir Stuart Rose, M&S executive chairman, urged staff to stop leaking information about company matters after he took charge four years ago.

Sir Stuart has suffered one of the worst years of his career. Institutional investors rebelled over his promotion to executive chairman in February and in July a profit warning wiped more than £1 billion off the company’s market value.

M&S has brought forward a key quarterly trading statement by a month, to October 2, in a move that has triggered fresh concerns over the group’s trading performance.

The Times revealed two weeks ago that M&S wanted to cut its redundancy terms by up to 25 per cent. The retailer’s own staff council, the Business Involvement Group (BIG), warned the board that the proposals had caused “unprecedented anger” amid the workforce.

In a memo, Malcolm Heaven, BIG chairman, told M&S managers: “There is zero confidence that we will not be entering another round of redundancies, and a strong suspicion that this is one of the reasons behind the proposal.”

He added: “There is a growing perception that M&S is becoming ageist in its approach and adopting a very short-term approach.

“This has also raised questions on the statement that we want to be the ‘employer of choice’.”

M&S watered down its proposals after The Times revealed the plans two weeks ago.

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