You most certainly CAN transfer BT to Virgin.
My folks did it over 10 years ago BT-NTL, and friends here have done it too.
( Dave Trouser ; the people's choice - 75% agree, Wed 10 Jun 2009, 19:38, archived)

Maybe it was just here
We didn't try to hard to be honest as I was getting narked with calls from the previous owner.
( Fluzzy namby-pamby pudding and pie, Wed 10 Jun 2009, 19:41, archived)

the old cabletel telephony system is very pants
and from what vm employees have told me, cabletel line cards hardcoded with numbers, only pure ntl area are able to do it properly

i could be wrong though.

hi fluzzy :)
( hooker1uk Filth monger of the lowest degree!, Wed 10 Jun 2009, 19:55, archived)

Sounds about right.

( Fluzzy namby-pamby pudding and pie, Wed 10 Jun 2009, 20:00, archived)

but NTL couldn't find their arse with both hands
All you had to do was tell them what to do and it worked.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 10 Jun 2009, 19:54, archived)