Just a guess
I was assuming that what the following Liverpool University website said was true (which may not be so) http://pcwww.liv.ac.uk/~Sinclair/ALGY399_Site/national_trust.html
Recent Acquisitions to the National Trust Holdings
....
1997 22 Forthlin Road - Paul McCartney's mother's house in Allerton, Liverpool - a typical example of a 1950s council house.