Just to finalise this thread - hate threads left open with no conclusion - I ended up speaking to JF Automotive in Maidstone. They managed to flash the original, not post dieselgate, firmware back onto the vehicle's ECU and re-enabled the DPF. All adaptions/re-calibrations carried out. They then flashed their Stage 1 tune on at my request, which has given the car more torque and top end power than deleting both the DPF and Cat. At their request, the car was returned to them one week later, just to make sure everything was okay and that no fault codes had appeared or were pending - all good. All for the princely sum of £295.
Suitably impressed with these people.
Thanks to those who chipped in with advice. It's appreciated.