Religion has become the butt of workplace jokes as workers who would never make sexist or racist comments mock belief instead, a survey has found.

A study by ComRes found that up to a million workers may have faced harassment, discrimination or bullying because of their religion or belief.

The report's authors suggested that this tended to be in the form of "lower level exclusion" which people did not bother to report because they did not feel it was serious enough.

Respondents said they had been made to feel uncomfortable by colleagues making jokes about religious beliefs.

Katie Harrison, director of ComRes Faith Research Centre, said: "Some people told us they felt uncomfortable about mentioning that they pray.

"Or we heard of people feeling upset that religion was the butt of jokes in a workplace where people have become much more aware about making disparaging comments about gender or disability."

One survey respondent said: "In our office, everyone is very respectful of minorities and would never be disparaging about women or people with disabilities, but when it comes to religion it’s fair game.

"People can be very insulting, especially when they express it through humour."

Ms Harrison said many religious people felt unable to tell colleagues that they had been to a mosque or church at the weekend and could not talk freely about the religious parts of their lives.