Tory MP Julian Brazier, co-chairman of the all-party Commons group on adoption and fostering, said: ‘I work with BAAF all the time and I know how much they bring to adoption.

‘I must say I am very sad that they should use this language about people who have an honest disagreement with them.’

Author Patricia Morgan, who has published a study of gay adoption, said: ‘It is disgraceful that they do not wish to discuss the pros and cons of gay adoption. They just go in for abuse. They do not appear interested in evidence about the outcomes for children. And it is a disgusting phrase to use.’