One in five MPs has suffered from mental health problems but decided to keep quiet because of fears of a hostile reaction, according to a survey published on Wednesday.

An anonymous questionnaire completed by 94 members of parliament revealed that 19 percent had personal experience of mental health issues, while 86 percent said the job was stressful.

"Greater openness at Westminster about mental health problems would have a significant impact in challenging stigma and discrimination," said Sandra Gidley, joint chairman of the All Party Parliamentary Group on Mental Health.

The survey, conducted by the parliamentary group with support from mental health charities and the Royal College of Psychiatrists, polled 94 House of Commons members as well as 100 peers from the House of Lords and 151 parliamentary staff.

It found 17 percent of Lords and 45 percent of staff had also suffered mental health problems, while one in three of those who responded said work-based stigma and concern about a hostile reaction from the media and public mean they kept quiet.

The report criticised a law which forces members of parliament to give up their seats for life if they are sectioned under the Mental Health Act, while an MP who is physically incapable of working for six months due to illness is not forced to stand down.

"When the former Norwegian Prime Minister Kjell Magne Bondevik publicly disclosed his experience of depression, it did not affect his popularity," Gidley said.

"He went on to be re-elected and proved that people who have experienced mental health problems can recover and manage a challenging job."

The charities said the government needed to repeal the "antiquated" law if it was to send a message to employers that such discrimination was unacceptable.

"These findings are an affront to democracy," said Paul Jenkins, Chief Executive of Rethink.

"MPs and peers need to be free to bring their personal experiences to their vital democratic role. Instead they are being gagged by the prejudice, ignorance and fear surrounding mental illness."