Even though Liverpool is full of empty buildings, there don't seem to be many or any squats. The closest thing are The Arts Organisation, who work in partnership with a landlord who owns several empty buildings in the center of Liverpool, to regenerate them for living, social and arts spaces.
Some speculate that Liverpool's squat scene is not vibrant for two reasons: that Liverpool's working class roots mean that there is resentment for those who get something for free (a place to live and work) that others work hard for, and second, that Liverpool is also a relatively small city and the lack of anonymity means that squatted buildings don't easily slip under the radar. Low rents could also have something to do with it.
With such a vibrant history of activism in the city perhaps it is time to create a Liverpool squatting culture - if a critical mass of participants took over buildings throughout Liverpool, police and neighbours might eventually become more accustomed to and accepting of the practice.
There were quite a few squats in Liverpool in the 70s and 80s, when the practice was most fashionable in the UK, particularly in the Liverpool 8 area. However, this largely died off the the 90s. One notorious 'occupation' in the 90s was of the Irish Centre on Mount Pleasant. When its owners tried to close it down, many people occupied it in protest for quite a long time, but to no avail. Though a new Irish Centre has since opened elsewhere in the city.
I would say cheap rents have a lot to do with it, and a lot of people rent property and then get away with not paying for it, but also the Council and property owners are quite good at 'tinning up' empty buildings. There are still many abandoned buildings in the city that are used by people that don't pay rent, however these are mostly used by addicts for crack dens and the like. Another factor is that most of the abandoned buildings in Liverpool are in very deprived areas which can be dangerous even for native residents, and most 'art people' would be to scared to occupy them for fear of being beaten/robbed etc whether misplaced or not.