WIthout asking him, I would guess he is some kind of security guard? He is probably situated at the entrance to stop people running out with shoplifted goods.
My guess is that he's a greeter. His job is to smile benignly at customers and say g'mornin'. Quite what this achieves is beyond me, still.....he looks chirpy enough.
OOOOps have I missed something here - he (and it shouldn't just be Men) acts as a Commissionaire - he should always have a friendly smile and a welcome basket for you and advise you if you have any problems, where to take them to - and I have to say the more these supermarkets - not just Tesco - Asda is very good! - employ these older members of the community - the more I am Pleased - one to give them something to be proud of doing and earning a bit of a wage but also to get them out of their 'wives -partners - husbands' hair for a few hours of the day!!!!!