Assure him by wearing lots of safety gear. By safety gear I mean a mask and a load of old cheap canvas BDUs or a set of heavy overalls or a burlap sack or something. It's pretty much only your eyes, teeth and exposed sensetive areas (neck, groin, etc) that need protecting, everything else will just get welts and bruises which will heal.
Also,
stay classy Britain. It's all I can get with my budget, considering how often I go to the pub. I only really want something to shoot a few cans when I'm bored, not like there's any actual airsoft sites for miles, and the farmers would shoot me with rock salt if I mucked about on their land with an airsoft gun.