When I called my local council and asked if I was able to carry out a PIR (not being registered with any scheme) they said I would not be able to do this as I'd need to be Part P registered to be able to issue the certificate
This has nothing to do with the Council and has nothing to do with Part P.
A Periodic Inspection Report is soley between the electrician and the person requesting the report. Between them they agree the extent of the PIR - it may be limited to specific circuits or the whole of the installation - its up to them and them alone.
That means that anyone can carry out a PIR.
However, whether a PIR carried out by someone without the necessary knowledge has any value is open to speculation and possibly challenge.