It's not the users of the trolleys, honest!
Shopping trolleys have developed individual and collective consciousness and are currently planning on taking over the world by means of a series of complex financial transactions.
The repesentatives of their species who operate in the arena of Tesco, Waitrose et al have a defined role within their communities to gradually cause chaos to our society by rolling everywhere in the locale and being found, on occasion some 3 miles from their base stations.
They have however, suffered numerous losses of late with a number of their kind falling foul of the local waterways and drowning in the Kennet and Avon where their lifeless carcasses remain.............