The UK Takeover Panel has given retail entrepreneur Philip Green 28 days to make a formal bid for Marks & Spencer or walk away from the UK retailer for six months.

The panel has invoked its "put up or shut up" clause under Rule 2.5 of the takeover code for Revival Acquisitions, Green's bid vehicle, to lay its cards on the table. He has until 12.00 GMT on August 6 to issue a statement to bid or not to bid.