Courtesy of GAME, Nationwide Paintball are offering free paintballing for up to 10 players with this voucher.
Just pay a £10 deposit (per person) which is refunded to you on the day in the form of paintballs. This also includes the admin fee.
This package usually costs £22 per head (equipment hire and 100 paintballs), so you can't really go wrong at £10 per head for the exact same.
All the links you need will be in the first comment.