Noooooo. Don’t cloud things. I was happy with the charger placebo!
Ok , so its just got stranger.
Car started fine. However, it wouldnt switch off. Put the key back of the “off” position and it carried on. Sounded a bit erratic , but carried on. Twist back to “on” - not start and it idled away happily.
Kill the engine by putting it to off and then disco the +ive terminal on the battery
Sounds like a relay pack misbehaving wont turn on, then won’t turn off
Interesting.
Any ideas which one / where to look / wack / set fire to ?
Sorry no 
No worries. At least I have an idea that its not me going mad.
When I came to restarting it , I couldnt get the damn thing restarted.
Found a work around.
Key in ignition , pressed the immo button to arm it . Twisted key , it squarked.
Turned it off.
Car started …
Smug mode on
Told you it was not the charger.
Smug mode off
However, how have you connected the trickle charger? If it’s via the lighter socket and it was powered on you may not be able to stop the engine.
Connected directly to the battery via fly leads.
Turned off and not connected when starting the car.
Don’t think anyone said is was the charger at fault? 
My initial thought was that it was one of the immobiliser relays (like you I’ve had immobiliser issues) not operating correctly which would prevent starting, but it could equally be another relay as ade suggested. MFRU faulty?
I tend to agree, dodgy relay, connection, earth etc. Don’t understand why it would not stop.
It’s due a service end of the month so I’ll request thr chaps investigate for me.
If you can think of anything in the mean time …
Today it started first time and stopped perfectly
Yesterday I did some science and wiggled some wires near the MRFU.
Ill see if it does it again and wiggle away again to see if I can solve it.
At least until it goes into the garage.
Do have a look at the MFRU. They are about £100 new but a scrapped one from a Rover should do the job. A faulty MFRU could (a) stop the engine starting and (b) stop it stopping once the engine is running. That was certainly true for lots of cars in the 80s and was how they got hot wired and stolen. The Lotus has an immobiliser that stops them being easily hot wired but a faulty MFRU may stop it stopping.
I would disconnect the MFRU and plug it in again a couple of times. The problem is usually the connectors and plugging in and out cleans the connections.
I had a nightmare problem with an S1 Elise which was the MFRU, it was cutting off too quickly when the ignition was switched off, that stopped the ECU setting the idle control valve to its home position. Being a stupid design it assumed the idle control valve was in the right place when the ignition was switched on again and the car would not idle.
Its the accessibility part I am struggling with. I dare not unplug it as I cant reach easily.
Is the rover part the same as the yota part? Mine is a 2zz from a s2 …
It has the same part number as the one used on the S1 Elise (see Deroure). It’s only a hunch AND the running on I know is possible on an S1 but I don’t know about the S2. Sorry, I forgot your car is an S2.
It seems entirely plausible and almost the same symptoms
After 6 months this issue has come back to haunt me!