If it is going to be returned in the UK there are several courier services. Parcel Force might be one place to start:
http://www.parcelforce.com/portal/pw...diaId=25800695
TNT might be another:
http://www.tnt.com/express/en_gb/site/home.html
Parcels 2 go another:
http://www.parcel2go.com/
I have never had cause to use them myself as I always use Royal Mail, but I'm not sure they are geared up to do computers. Just make sure you ask if insurance is included in the delivery price for the amount you state.
Good luck