External candidates being floated to take the helm at Morrisons include Sainsbury's Dido Harding and Mike Coupe, Asda's Darren Blackhurst and Andy Clarke, Tesco's Richard Brasher, and Stefan Barden, the chief executive of Northern Foods. John Browett, the chief executive of DSGi, who was highly regarded at Tesco before joining the electricals retailer, may also be approached.