Well I finally got the new modem installed yesterday, totally pain free and the Prem HD channels were on within the hour. The chap was even kind enough to make me a coax extension when I mentioned I wanted to move the extra Vbox from my bedroom to my son's.
Fantastic speeds so far, can't wait for the upload increase to 5Mbs, if it happens:
Now it's just a case of sorting a swap from the Vbox to a VHDbox, CS are still adamant it's another £49 charge. :/