I've just found this map on the Liverpool Film Office website.
http://www.liverpoolfilmoffice.tv
They say that Liverpool is the most filmed city in the UK after London.
https://maps.google.com/maps/ms?msid=206420232406992275861.0004d136f7861f53baa43&msa=0&hl=en&ie=UTF8&t=h&ll=53.429388,-2.943046&spn=0.119256,0.210634&source=embed