Deer hunting or stalking?
Stalking is with rifle, hunting with horses and hounds.
If you are talking about stalking then you need to learn to shoot if you don't already. It is possible to buy a stalk with rifle but more commonly you take your own, so this means firearms certificate with suitable rifle and expanding ammo. Suitable rifle depends on your quarry but south of the border would be .243 caliber.
Various places offer days stalking, usually you would be out with a ghillie or professional stalker. You would need a fair bit of experience before you would be allowed out on your own, in fact some constabularies will insist on a period of accomanied rifle use.
Stalking 'qualifications' such as DSC 1 which Burnt Ash refers to are required by some places before you can stalk but not all by any means. Some constabularies insist on it, but this is not strictly speaking on the level. Personally I would make sure I was a member of BASC and challenge such a condition - but I am an awkward bugger!
Stalking ain't cheap!
Before you even set glass to beast, you've the costs of getting a FAC, buying your rifle, buying a scope etc and then you need to find a stalk.