Todd Adkins, of the University of Notre Dame in Indiana, said audiences seemed to turn off their critical faculties when they reach the cinema.

‘Viewers come expecting to be entertained and are not prepared to encounter and evaluate political messages as they would during campaign advertisements or network news,’ he said.

Dr Adkins’ research, published in the journal Social Science Quarterly, was based on a study of 268 students who were asked about their political views, shown a film and then questioned again.

Half identified themselves as politically conservative.