Link: Macclesfield MOT & Service Centre
Thank you to everyone who replied.
We removed the vapouriser (which on these isn't easy as driveshaft is in the way!) and found the end to be completely blocked up as several of you mentioned. The local Ford dealer had 28 in stock so looks like a very common problem!
Forced a regen and this time it successfully completed. Pressure readings have come down, perhaps not as low as we would like, but will see how it goes on under use.
Thanks again.
Sean