Thomas Cook have operated A330`s into BFS before although they aren`t that common.
In the past they have been used on routes to Florida,Dominican Republic and Barbados,Cancun etc.
Often they come in with a partial load from Glasgow,Manchester or others before heading on to their final destination.
I should have some pics of previous examples.
If the one you saw parked behind the tower,it`s almost certainly a troopflight.
Pic of G-MDBD in the gallery A330-243 from June last year.