Officially, you should get Virgin out to do it.
Unofficially, as long as you don't get muck/water into the connectors - I'd just do it.
Make sure not to pull hard or lay with any extreme bends. If it's not already ducted, it might be a good idea to consider that (that said, Virgin rarely seem to bother)
If you've got the normal coaxial shotgun (with 2pair telephone) cable, you'd have to re-crimp with jelly connectors at the external box, so best to give it a miss if unsure.
Tom