I disagree with Wordy. They are actually very easy to take care of. I had one when I was young, it had escaped from it's prior owner. They are an endangered animal though, so the only legal ones are from breeders. Unfortunately you will have a much more difficult time with a tortoise, since you live in the UK. I live in Southern California, so I have an appropriate climate for one. You will need heat source(s) and a very large tank to keep it in. Also it should be noted that a tortoise can easily outlive a person, so care should be taken to make sure that this is a pet that you want for the rest of your life.

 I found a desert tortoise one on the road...in my neighborhood. He must have escaped because he was crossing the street amidst traffic. I wrapped him in a sweatshirt and took him in. I took care of it for a few days while trying to find it a home. It wasn't hard, considering I have a huge back yard with dirt, plants, a pond and grass. I read on the Internet what to feed him. I was worried for him and for myself as I was told that it is illegal to keep a desert tortoise. I did find a tortoise sanctuary in Arcadia, CA that was willing to take him in. When they did, they said he was VERY old! Last I heard, he was having a good ole time in Arcadia.

 Tortoises can't be imported into the UK anymore, and they are hard to breed here, so you don't see many. There are a few online companies that sell captive-bred ones - here is an example - but it could be a good idea to look for a forum or owners' club - if you put "tortoises uk" in a search engine you can find some links - and chat first with some owners. Then maybe you could get a personal recommendation as well as care tips -they can be tricky to look after, though they do make lovely pets.