Back in the office, All fixed on the side of the road

It was the brake pedal switch, it wasn't working properly and the brake lights worn't working either. That switch tells the solenoid on the gear lever to un-lock so its definately an electrical system and not a cable.
I took the switch out and cleaned it up (luckily had an electrical tester on me) and it worked fine so re-installed it and hey presto.

Also, if this happens to anyone else you can remove the 10AMP 'STOP' fuse from the driver foot well and it over rides the system and lets you get the gear out of park. It disables the brake lights though so only do it if you have to !!!!