DND would be better served by BE to LTN or LGW.
Look at the other domestic routes tried and failed to/from LCY:-
PLY, NQY, CWL, MAN, NCL, LBA, JER
The only domectic routes that last at LCY are GLA and EDI - mainly due to VERY significant corporate traffic and large VFR markets.
DND has neither.
HIAL should be strongly courting Loganair (as BE) to operate DND - LTN.