Thanks very much Jerry, that all makes sense. It's the first time that I've encountered the problem, good to know it's not that unusual. I book my tickets online through the oneworld.com site - how would I book the flight on oneworld.com so that London was a stopover rather than a transit? An overnight stay would solve it I guess but is there any other way that I'm missing?
I'm a poor packer as my wife points out so I usually have a suitcase of some sort with me but I can see why that creates the problem.
Touch wood my concern about BA losing my bag may have been overdone, my bag is currently sitting at T5C at Heathrow according to its Airtag while I'm at T5A - no mention of strikes at all :-)