don't you buy a headset for 20 pounds. certainly not a wireless one. you'll get bad sound, range, bad quality and will have to buy a new one far to soon.
depends how much cash you want to dish out for them... I'm looking for a set atm, but in the £150 range... :/ For £20 you wont get much in the way of decent durable wired headphones, let alone wireless, but if you can stretch a bit, the Plantronics Gamecom 377s are the best low price headset i know of. my bro has a set. Good sound (for the price), well built, good mic and very comfortable.