Incase this is useful for the next person.
The car had done about 44,000 miles, so I wasn't expecting gearbox issues.
Apparently it is a common problem in DSG 7 units.
I sent the mechatronics unit to a company called ECU testing, a mechanic was able to take it out and sent it off to them. It cost £400.00 including VAT for a rebuild of the unit which comes with an unlimited mileage warranty. It some back within a week and has since been fitted and the car drives.
I am suspecting, after talking to an experienced mechanic, it could have been a cracked hydraulic accumulator, which would have been cheaper to fix, however, ECU testing fix this and complete the rebuild.