Hi there,
Beautifulgirls has given some really great advice - especially the mention of the Tortoise Trust, who are a true authority on best tortoise keeping practice, but I would argue that there is absolutely no reason to keep a hatchling indoors for a few years. My hatchlings (I breed tortoises myself, but sadly not in the UK anymore) thrive on as much secure, sheltered (both from extreme sun in the summer, and from damp and cooler nights) outdoor time as possible, right from day one - literally!
A tortoise that is reared with as much access to the outdoors (while still always remembering that no tortoise species will have originated from a climate that is the same as ours) will do far better than any one that is kept exclusively indoors for any long period of time. There are the well known physiological benefits (mainly the availability of natural UVB, rather than from artificial lighting sources) but there's also a huge difference psychologically, in my experience, because of the larger space that can usually be dedicated to an outdoor enclosure, and the potential for boredom release and natural behaviour that comes from being able to forage as nature intended, rather than having all their food "served up" in front of them, and with them then left for the rest of the day thinking...hmmm...what to do now??
Sorry for the ramble, but what I'm basically trying to say is don't even consider a tortoise as a pet unless you plan to dedicate a decent sized portion of your garden to them...they are not an indoor pet (I know that you, Bobbalina, never implied that you thought they were, but you average, crappy death-store (sorry, reptile-store) will invariably sell you a sick import while saying that's fine, along with selling you a "vivarium" for them and a tub of pellet "tortoise"-food... )
I was about to write more when I remembered that I've already replied to similar threads before, so please can you just read my contributions to the following threads? (I'm lazy, so shoot me LOL!)
www.mumsnet.com/Talk/pets/762281-getting-a-tortoise-advise-please
www.mumsnet.com/Talk/pets/807720-Tortoise-Tips-Anyone
I've put me email in those previous threads - I'm still happy for people to email me about anything tortoise-related.
Hope this helps?