Bentley S1 problem...

....recently started (with difficulty) a '56 S1. It's been standing for a
while and needs to be moved under cover.

After a lot of trying, I got it to start but it didn't want to tick over so
I let it run at slightly higher revs for a couple of min's. Tried to open it
up more but the engine wouldn't respond. Oil pressure was reasonable (dial
showed just under half way) and it was starting to warm up. The engine was
clearly not running on all cylinders so I stopped it and cleaned the plugs
(again) two of them were badly sooted up. Then having restarted it, it
seemed better (but still wouldn't run on tick over) so let it run at
slightly higher revs for 10 mins or so. Engine was coming up to temperature,
oil pressure still ok. Then it backfired (or at least made the noise of a
backfire) Then a couple of times more (but less loud), then stopped. There
was no smoke & it restarted briefly and then stopped again and now I can't
even get it to turn over.

The ignition lights come on but there is a low humming noise coming from
somewhere when switched on (can't tell where) and it won't turn the starter
motor at all.

Any ideas gratefully received. Trying to get an auto-electrician out but
having trouble finding one interested in old timers.