I'm a little confused by what you are asking. To get back to basics if the set was 'pre-tuned by the shop assistant' we have assume that this is in the same area as you live and therefore tuned to your local transmitter.
In order to watch the Freeview channels you need an external tv aerial attached to the aerial socket of your TV. In order to receive the Virgin Channels you need the appropriate box supplied by Virgin and a subscription. This will be connected to your TV via a SCART Lead. The Virgin cable system does not provide any access to the conventional digital Freeview services. In some areas there was a free access to analogue TV, but this is gradually being discontinued.
You cannot get Freeview through the SCART lead. There is really no need to plug an external aerial into the V-box, plug it straight into the TV.
A websearch reveals that there were a number of problems related to this set, particularly in relation to the Freeview tuner cutting out. This was about 2 years ago so, hopefully this matter has been resolved. At least you have access to cable tv so the loss of Freeview is not such a tragedy.
http://www.digitalspy.co.uk/forums/s...d.php?t=487589