When insulating the loft, take the opportunity to protect the water tanks and pipes as well. The water bylaws now actually require tanks to be insulated.
The cold water storage tank and the expansion tank for the central heating should be insulated, as should the hot cylinder (in the airing cupboard). Purpose made jackets are available which make the job simple and effective. They consist of an insulating blanket wrapped in a plastic cover. These are positioned over and around the tanks and held in place with ties.
Remember - take a note of the tank sizes so you can get the correct size jacket for the job.