Luke lives in stoke-on-trent, not gloucester.
Just done a search on BT.com an the address you give there doesnt exist either. There is no Malpass that lives at that address.
You have been scammed, but not by the Luke Malpass on here, by someone pretending to be him maybe.
Personally i dont trust anyone that offers a cashiers cheque. When my bro was selling his moto-x bike, he kept gettin people asking if they could pay with a cashiers cheque, also asking for our postcode to put into an address finder, we found out that the cheque would bounce an the postcode was to put into a sat-nav so they could come steal the bike. This has been going on a lot.