I use the following:
http://batterytender.com/battery-tender-plus-12v-at-1-25a.html
Used them for years to keep vehicle batteries up to par at all times.
Have leads permanently attached to battery so when I pull into garage, all that is needed is to connect the tender to the leads, and the battery will be maintained.
When ready to go on the next outing; just unplug, start up, and go.
Battery is always in top shape.
Have had batteries last 7 + years using this method.
I am sure they are, or a similar product is available in the UK.

Past The City Limits