Sontosean
BA used to operate twice per day to Nairobi with a day and overnight flight with 747 then 747 / 777 combo. Kenya just one service but I never used them on that route but have used extensively in East / Central Africa.
As for Mombassa I remember Monarch going in there along with a number of other European smaller carriers and Qutar used to go in from the Gulf.
Currently Condor stop in on the way to Zanzibar along with aforementioned European charter carriers. There is quite a large Italian community so a number of flights from there as well as further north in Europe.
I think Kenyan may have done a flight to AMS but it may have stopped in Nairobi on route but I don’t remember a LHR service with out a change of A/C but you can check bags through obviously with them.
I / we fish and dive in the Malindi area up the coast from Mombassa so know the area quite well over the last 20 plus years . However I tend to try and fly into Malindi direct from Wilson or Jomo as the road can be interesting to say the least, and that’s after the relatively recent improvements, before that it was a bone shaker, and at night a little dangerous re accidents.
Cheers
Mr Mac