550 starting problems

My 550 has intermittent starting problems - on key turn sometimes it fires up perfectly, other times nothing (no engine crank and some of the dash lights go out!). I’ve tried different fobs (even the red one) and that makes no difference.
Any ideas anybody?

Sounds like a stuck starter motor. On my old Defender I give it a few taps to free it up.

Could also be new fuseboard time, mine has issues