I too was just about to book LGW to MLA in September when I picked up on the Excel Airways substitution for some days a week. However, you can only ascertain this from checking the operator in the BA Timetable by clicking on the small aircraft symbols for each day of the week.

If you blithely go through the booking pages for a Traveller seat it doesn't mention Exel Airways anywhere - all flights ( including the Excel ones) are only showing GB Airways as the operator right up to and after the Confirm Reservation pages.

This seems to me to raise some interesting policy issues . Some would regard it as clear misrepresentation. Perhaps more importantly:

Is Excel Airways classed by BA as a Franchise Partner (it is certainly not listed as such) ?

Are their operating and aircraft standards approved and independently checked by BA? Or is it just up to GB Airways to trawl for a charter airline that can be passed off as a schedules BA flight?

Doesn't BA have a clear duty to make it very obvious to the layman that this is not a BA flight in any shape or form?