Adrian F - thanks for the suggestion about entering the frequency with the negative offset applied. The standard manual tuning mode on these TVs uses the analogue channel numbers (Ch-62, Ch-64 etc) and this is where the TV fails to detect the digital carrier. It is possible, however, to select the frequency (shown in kHz - eg 802000) and so it should be possible to enter the correct frequency with negative offset and see if the TV locks onto the Freeview Mux. Since I had already contacted Sharp and received the CA card, I ran the software upgrade instead (takes only two minutes) and confirm that the BBC North West channels can now be received!
When the final DSO step takes place in just over a week I will delete all channels and run a manual scan on the new set of Winter Hill frequencies to avoid the duplication that can occur with an automatic tune, especially since the Moel y Parc frequencies are first to be scanned. Cheers - Nick