The polling station, in a Tesco in Thornton Heath, south London, is the first of its kind in the capital, following earlier experiments in local elections on the south coast.
The Minster Without Portfolio said it was "a pioneering experiment" and said the idea could be extended across the country if it succeeds in boosting turnout for the 7 May council elections and referendum on a mayor for London. He was pleased by the reception given to the "shop and vote" scheme by customers he spoke to as he toured the store with the Croydon North MP, Malcolm Wicks.
But Mr Mandelson may have been less pleased with the way some of them planned to use their votes - with several plumping for his arch rival, Ken Livingstone.
Mary Elliott, 54, said: "I think I'll be voting for Ken, I've got a very soft spot for him. I told Mr Mandelson he wasn't socialist enough for me and said to our MP I voted for him because he's a socialist, and he joked that I'd better not tell Mr Mandelson that or I'd get him into trouble."
Terry Streeter said: "I'd like to see Richard Branson for mayor, but I'd be surprised if he stands. If he doesn't, then Red Ken, though I don't suppose Mr Mandelson would be pleased to hear me say that."
Mr Mandelson avoided the question of whether the party leadership wants to keep Mr Livingstone off the ballot paper. He said: "The first thing people have got to do is vote to have a mayor at all. First things first."
Asked if the pilot project was not turning the election into a promotional opportunity for Tesco, Mr Mandelson said he would be happy to see other supermarket chains getting involved.Reuse content