Where I live, you can't swing a dead cat without hitting half a dozen self-serve storage facilities. My understanding is that as long as you pay the monthly fee, they'll rent you the unit until Hades is covered in glaciers.
Google "self service storage"
Results 1 - 10 of about 24,700,000 for self service storage.
You're in the UK? Google "self service storage UK"
Results 1 - 10 of about 1,210,000 for self service storage UK
A couple picked at random:
http://www.bigyellow.co.uk/
http://www.sparkfordstorage.com/
and the trade associan for Self-storange companies:
http://www.ssauk.com/
Are you looking for something other than your normal self-storage facility? Google "high security storage UK"
Results 1 - 10 of about 10,100,000 for high security storage UK.
Good luck!