I can recommend Skirmish Wycombe in High Wycombe. Not too far from you.
Just to ram it home even more...
Rent for your first 3 games (at the same site) Then you can get UKARA registered and look to buy the toys.
- First get good boots with ankle support.
Either army surplus or more modern comfy ones.
- Secondly get good eye protection. (full face or separate lower mask is recommended to protect the teeth)
Aim to spend around £40 or so for good eyepro and some anti-fog wipes. (Someone chime in with the best)
- Don't bother with a pistol until later. They are fun but add extra hassle to loadouts, need more preparation and not that important for woodland games.