Marks & Spencer will next week try to force Philip Green to make a formal bid for the UK retailer or walk away. It is understood the stores group will ask the Takeover Panel to invoke its "put up or shut up" rule shortly after it outlines its operational strategy to shareholders on July 12.

Under the Takeover Code, Green will then have four to six weeks to declare whether he will make an offer or walk away for six months. If he intends to bid, he has a further 28 days to table an offer.