My 13 plate Octavia 1.6 Diesel engine keeps running when the ignition is turned off. It only stops when I remove the key. Any ideas what the fault could be?

many thanks in advance 

Relay or stop solenoid? No idea if that’s still a thing on modern fuel pumps mind...

Thanks, it’s been doing it all day and now I’ve just had a message saying “starter system faulty, workshop’

I was thinking "anti-diesel valve" but that's potaytoe or potahtoe with your other reply; we both think the same component has failed to operate correctly.

Just realised I didn’t update. It was a faulty ignition switch. Thanks