Corporate affairs manager Martin Venning said Tesco would stick to secondary trading sites as it rolls out the small store format which has, so far, been used on Esso and own brand petrol forecourts.
The first standalone Express will open in Southborough this October (The Grocer, June 15, p4) and the second in the suburbs of Manchester in late November.
But City analysts said Express will never be a lucrative business proposition.
One commented: "Express is a nice afterthought from the point of view of customer convenience, but hardly a mould-breaking profit opportunity.
"We have heard Tesco wants to roll out stores at the rate of about 100-plus a year. If you do the sums on 50, they perhaps take Â£50,000 a week each, that's Â£2.5m in total, the same as two very good superstores."
Another added: "There will be problems with operational economics. Tesco is geared up to deliver in lorries to shops the size of factories. Now it will have to deliver a Ford transit-sized amounts to broom cupboards."
Prices will have to be put up, he said: "Tesco has struggled with pricing on Express forecourts. We are likely to see a couple of per cent premium over the big stores."
Association of Convenience Stores public affairs and communications spokesman James Lowman said: "Tesco's move into convenience shows how vibrant the convenience market is, but multiples which move into small stores take a while to get it right.
"Locally, Express will be a threat, but independents can fight back as they know the area better. They need to market their stores on points of difference from the multiples."