Many thanks for your detailed reply.

There is a lot for me to work through. I find it very confusing (perhaps that’s the plan) dealing in all these virtual currencies (FB Miles, Accor Points and their combinations with cash) to know when I am getting the best value.

I managed to link my FB and Accor accounts together. Not signed into my Accor account for many years and lists only 1 night at an ibis in 2017. Perhaps, it is best to transfer FB Miles over to Accor Points (is 1000 FB Miles -> 4000 Accor Points deemed good?) and redeem them for London hotel stays.