Virgin's 10Mb service that's being upgraded to 20Mb is most likely cable (co-ax). It's certainly not ADSL, and unlikely to be fibre-optic to the house.
Our Virgin cable domestic service has recently been upgraded to 20Mb from 10, and I'm getting 17-19Mb on one wired PC and one wifi PC, but 2 wifi PCs further from the WAP are getting between 8 and 12Mb (802.11g). One was only getting 2-4 until I replaced the antenna on the NIC with an external antenna further from the PC.
Wireless throughput does drop off rapidly as signal strength decreases.
SD