Discovery 2 Starter - Can't stop, addicted to the shindig

First post, so be gentle if I contravene any rules.. ;-)
2004 Disco 2 has flat battery. If that was the only problem, well, I wouldn't be here!
The good lady told me the other day that it wouldn't start, so stopped trying before battery went flat. As she was walking away with key in hand, the starter was still turning! It was "nearly flat" by then so didn't turn for long.
Needless to say, when I got home, it was completely flat - not even dash-lights. Nearly fried my charger when first connected, so disconnected the -ve and re-charged battery. Touching the terminal results in arc-ing and starter turns - key was in ignition, but turned off. All I have tried so far is swapping the Starter Relay R2 with R3 in case the relay was stuck/broken.
Is this likely to be an ignition switch issue, or where do I look next?
Any help would be gratefully received.
Thanks,
Peter

Hi buddy sounds like the starter solenoid is at fault

Welcome to LZ btw !!

+1 wot kevstar said.

Easy to check. There are two wires to the starter motor, a heavy red one direct from the battery and a thin Brown/Red wire which activates the solenoid coil.
If you disconnect that thin wire and the fault persists then it's definitely in the solenoid. Sounds like the contacts have welded themselves closed due to arcing.
The solenoid can be rebuilt from underneath without removing the starter motor, but it is a bit of a faff and fiddly.

Thanks kevstar & brian47 - will check out the starter solenoid. Sounds obvious when you say it.. ;-) I had thought there may be some other isolation if the ignition was off, but I guess if the 2 wires are pretty much straight from the battery, if the solenoid is closed, the motor will turn!
Will let you know how I get on.

Quick update: removed the Starter at the weekend; solenoid was "free" by the time I got it off, but one of the contacts had a copper "pimple" and the copper disc part was rough and pitted. Couldn't get a service kit from the local factor, so stripped it down and filed contacts and disc smooth. Put it all back together and it all seems fine now. Thanks again for the quick diagnosis!