ISTR that when I suggested a rout to MLE several years back after our honeymoon, it was rumoured there was a problem with the MTOW of the aircraft on the return - not enough fuel could be carried to get you back to the UK without risking a dip in the Indian Ocean at the end of the runway.
http://www.flyertalk.com/forum/7668842-post17.html

I know Qatar and Emirates do land large jets there, but they are only for relatively short 4 hours hops and the UK charters are 757's or similar.

So MLE may exclude itself on practicalities....

NGBTS