Thanks for all the replies , i did think it was the case that Kenyan previously cleared LHR before with their last B737 batch and also i believe Ethiopian also did the same ; assumedly for the same reason of a station.
I'm not sure if any of these flights onward were direct revenue flights or not.Certainly Monday's fight on to Kenya via Cairo was empty.
It just would be nice to have an advanced notice of these sorts of thing dropping in to LHR.