GLA-DUB via LDY
Yes it is bookable through BA.com and it is shown on the website as 2 seperate flights
However when you check in for the first leg you would be given your boarding card for the second leg meaning you would just have to go straight to departures. I am unsure of check in closing times in LDY, but I am guessing that by the time you landed in LDY and made it through arrivals the desk would be closed.
Dozens queued to go through departures - obviously travelling with FR and not BA/Logan as the SAAB I am sure only holds 34.
Also agree with what others have said, Loganair are one of the finest airlines I have ever flown with. It is also worth bearing in mind the areas in the Highlands & Islands that they also fly to and from, these areas have some of the most challenging weather on the British isles and they are well clued up, if not better than most on what to do and how to deal with flight dispruption.