It makes sense to but the extra 1 weekly into Heathrow, but the question is why have they not done this already then? Difficult slot time
Depends on what the old bilateral allowed? may have been for 13 weekly flights. Slots and eqv may be an issue however.
Last point, does the 332 have sufficient legs to do Colombo - Manchester nonstop
The A330-200 should manage MAN-CMB no problem at all.
if it is to be operated by A330s, where would they come from as they do not have any on order
They already have an A330. Just search for 'sri lankan A330 at manchester' into google, and Im sure lots of images will appear. It was at MAN for about a week before it went to UL. They may even have more.