I have bought a Motorola mobile at Tesco and have gone to charge it but it is only a small plug and my normal sockets are too big .Any suggestions ,other than ask at Tesco tomorrow .
As JimF suggests, it's likely that the charger unit has a travel plug, where the big earth pin can be moved downwards to make it easier to fit into a bag. Simply pulling that pin upwards is likely to solve your problem.
You probably don't need the charger unit anyway. The cable that plugs into it (with your phone on the other end of it) can be plugged into any USB socket, such as one that you've got an old charger.