Marks and Spencer has chosen the former finance boss of books and stationery retailer WH Smith to replace Ian Dyson who's off to take the top job at Punch Taverns.Alan Stewart, chief number cruncher at Smiths between 2005 and 2008, will join M&S by the end of October. Dyson steps down on 31 August after five years at Marks.Fifty-year-old Stewart is currently chief financial officer at Irish aircraft leasing company AWAS, who he joined April last year. The former investment banker at HSBC has also led Thomas Cook UK and been group finance head of Thomas Cook Holdings."Alan has an impressive track record and will be joining us with extensive experience of retail and other highly competitive industries including travel and banking," said M&S chief Marc Bolland, who's only been at the company three months himself.