Update. Seems to be confirmed as electrical. I put it in 3rd and rocked it and the aux belt has moved.
The garage can't pick it up until Monday, so I'll just have to wait. It's sat on the drive looking sorry for itself!
Jack it up, and put power to the solenoid mate and see if it turns over then.
If so then you know that when you turn the key its not getting power to the solenoid.
So then you can work back from there, its quite probably the wire from the relay to the solenoid rotted, especially if you have run without arch liners (because racecar)