usually on a Domestic Run
Your use of the word "usually" is misleading. BMI have enough issues without people implying they routinely use heavies on the domestics. BA occasionally use the B777 on the LGW domestics, but *ONLY* when something has gone awry and rather than cancel the flight, they use whatever equipment is available. This is an admirable trait of a good airline and whilst I don't think BMI are as good as they were, we should bear the above in mind.
On the June 21st onwards it was used EDI/MAN-LHR for a 2 week period.
Which A330? The ACARS for all three, G-WWBB / D / M suggest otherwise. I can check the logs from lhr-lgw.co.uk tonight, I am curious but sure you are wrong.