Hi all - Just an update on this. The PCN has been cancelled ! The reason they gave was because they did not reply in time. I actually got the letter by email after midnight on a Sat (so am guessing it was a system issued one). Am not sure if it was the reps I made above or indeed their lack of reply (or both) but something worked. I've attached the reply here for future use so it can inform others. Have left out the name of the Process investigation Team Leader for privacy in case.
@Hippocrates - thank you for your reps wording and advice from previous cases which came in very useful. Happy to forward you the full letter if helps, just let me know.
Thanks again to everyone else on here who responded and for your excellent advice, much appreciated. You all are very decent people to take so much time out of your life to help others in stress.

