I do not know how many A330s fly from East Coast to UK but is there any chance it was wet leased Evelop flying for BA? It is already some time since I prepared A330 and it is really long time since I prepared empty A330 but if I remember correctly A330 has problem to fly empty because without load you are out of trim or almost out of trim.
As far as I know certain A330s and A340s flying from US to Europe they are simple to load but they can get tricky when you have few PAX on board. Then we had problems all the time with those birds. It really depends what was loaded in holds.
Typical scenario during winter for us was full first class, business and some people in economy. This makes you nose heavy. Then it depends what load you have. If you have just bags it may not be enough. If you have cargo it may help you or it can make things even worse. Why? Many light pallets do not help you in the aft so they go to forward making it even worse. Heavy pallets. Great, they can go to aft. Well, they could but you will not lock them there unless they prepared specific combination. Another thing which can mess it up are all the limitations for dangerous goods and special loads and sometimes locks were problems so you really could not load things freely. It happened to me few times that I had to move some PAX in economy to very aft. And by few I mean few rows. Well, many rows. Poor people were siting at toilets in aft galley just so I could let them fly with trim just on front limit.