sandyRoe, Uncle Ben do a pack of 'boil in the bag' rice, where each bag is one portion. I get this in B and M Stores, Morrison's also stock it. I think the portions work out around 30 pence each, so a handy thing to have in the cupboard.
Sandy, if you really don't want to use it all, open the bag and boil half of it in a saucepan, as per normal. Put the rest of the uncooked rice away for another time.