And the British Airways size limit is 22 x 18 x 10 in old money. That will be fine, it's a bit over on length, but under on the other two, so in Group 1 that will be fine. At the LHR gate for EDI you will have the option of surrendering the bag for delivery on to the carousel at EDI but that will be voluntary in your case and will allow you to stay airside at T5. It won't be checked for size, BA very rarely does that, your chances of that happening are well below 1% and in any event they'd let that go.