PHILIP Green and M&S boss Stuart Rose are heading for a showdown in a third and final bid for the Marks & Spencer group.

Billionaire entrepreneur Mr Green has agreed with a takeover panel that he must announce a formal offer for M&S by noon on August 6.

Failure to do so would rule Mr Green out of bidding for the retailer for the next six months.

Mr Rose, M&S's chief executive, will fire the opening salvo on Monday when he unveils his blueprint for transforming the flagging high street chain.

Depending on how that business plan is received by the City, Mr Green will decided whether to make one last bid for M&S.

Mr Green has already said he is willing to pay £8.4bn to take over the retailer, but has made a formal offer conditional on the support of the M&S board.

His overtures have twice been rejected by M&S, which said the proposal significantly undervalued the group and its prospects.

The battle for control of the retailer began on May 27, when Mr Green announced his intention to make a possible offer through bid vehicle Revival Acquisitions.

The latest move is aimed at lifting uncertainty from the retailer that could otherwise drag on for months.

In a statement to the stock market, the Takeover Panel said both M&S and Mr Green had agreed to the decision.

"No extension to the deadline will be granted, except with the consent of panel executives, it said.

Mr Green said the deadline increased the urgency for disclosure of details of the M&S pension fund, the latest annual report for which revealed a £670m deficit.