A senior Labour MP has said he was “appalled” to discover that his colleague Rosie Duffield felt unable to attend the party’s annual conference after she was made to feel unwelcome because of her views on trans women.

Duffield, who received threats and was branded transphobic after liking a tweet saying women were people with a cervix, has confirmed she will not be attending the conference because of the controversy generated by her remarks.

Pat McFadden, a shadow Treasury minister, told Sky News on Sunday he was appalled that Duffield did not feel able to attend the conference and said the party had to find a way of allowing people to debate difficult issues without resorting to abuse.

Duffield, the MP for Canterbury, has a record of expressing gender-critical views. She used an interview with the Sunday Times to say the row about her stance – in which she has been fiercely criticised by trans activists and abused online – had left her exhausted and at times frightened.

But she said she “mainly took the decision [not to attend conference] not because I really thought I was going to be attacked, but because I did not want to be the centre of attention”.

Sadiq Khan, the Labour mayor of London, said he thought somebody who professed the same stance as Duffield would be welcome at the Labour conference.

In an interview with the BBC’s Andrew Marr, he said: “It’s unacceptable that anybody feels unsafe going to Labour party conference, whether it’s Rosie Duffield, whether it’s journalists or anybody else. We must be able to have this conversation in a civilised way.”

Khan, who like McFadden did not endorse Duffield’s views on trans women, went on: “One out of four trans teenagers tries to kill themselves. These are one of the most vulnerable members of our society and it’s really important we have this debate in a cool, calm, respectful way.”

In a separate interview, Ed Davey, the Lib Dem leader, defended the party’s decision to ban a member from standing as a parliamentary candidate for saying women had to be female.

While refusing to comment on the particular case, Davey said: “The issue that we have been really clear [on] is that a trans woman is a woman and a trans man is a man. That is the issue that we’re fighting on. We believe that trans rights are human rights.”