The car decided to start today after 3 days(!), took it straight to the mechanic. Told him some of your ideas guys, it might take days to get it sorted though. I will keep you updated.
After turning the car off, the fault came back on soon as it was locked, so mechanic saw it as well. We'll see, fingers crossed. Soon as this is sorted I'm probably going to sell it as I honestly can't trust this machine anymore.
Tell whoever buys it though. Don't drop the problem on to someone else.