Tackling the growing abuse and intimidation of MPs does not appear to be a “high priority” for party leaders, the UK’s standards watchdog has said.
Lord Evans, chairman of the committee on standards in public life, said leaders must set a better example to their supporters on social media.
Kim Leadbeater, the sister of murdered MP Jo Cox, said she was very concerned about politicians’ physical safety.
Both were giving evidence to the Home Affairs committee.
Prime Minister Boris Johnson has called for all sides to “calm down” after a row over the use of inflammatory language in the Commons, in which he was accused of using “dangerous” words.
But the PM insisted he had been a “model of restraint” and the government plans to create a new criminal offence of intimidating candidates and campaigners in the run up to an election.
Labour leader Jeremy Corbyn has singled Mr Johnson’s language out for criticism, while arguing that all MPs need to do more to moderate their behaviour.
However, neither he nor Mr Johnson have signed up to a draft code of conduct drawn up by the standards committee aimed at improving the “intimidatory, bullying and abusive culture” in public life.
Speaking to the committee, Lord Evans said parties had not been “beating a path to our door [which] would suggest this is not top of people’s priorities at the moment, which worries me”.
He warned against being too “nostalgic” about the standard of political debate in the UK, which he said had always featured personal attacks.
But Lord Evans said the “abuse and intimidation” had got out of hand in the past five years – driven, in part, by social media, and it was threatening democracy by deterring people from standing for election.
His own committee had heard some MPs had even been scared into changing their votes on Brexit – something that would have concerned him in his previous role as the head of MI5.
“We would have seen that as a really serious national security issue, if it had been another state doing it,” he said.
Lord Evans argued social media companies had to do more to stamp out abuse, but the tone set by political leaders was “critical” as it gave “permission” to their supporters to behave in certain ways.
“It’s not evident that ensuring the tone of debate is appropriate is a high priority at the moment for a number of people in leadership roles,” he added.
The standards committee has joined forces with the Jo Cox Foundation – set up after Ms Cox was was shot and stabbed in June 2016 while on her way to meet constituents.
The foundation is holding meetings with senior party representatives to persuade them to sign up to the draft code, but so far, only SNP leader Nicola Sturgeon has signed.
Catherine Anderson, chief executive of the foundation, said: “We are particularly worried for people’s safety, that’s the immediate concern.
“With a potentially very imminent general election, we are very concerned about increased incidences of direct physical attacks.
“We know in the MEP and the local elections earlier this year we saw an increase in actual physical attacks, often against women candidates.
“We are also very worried about the importance of language, and the offline consequences of the language we are seeing online.”
Ms Cox’s sister, Kim Leadbeater, also gave evidence to the committee.
With her voice cracking with emotion, she said: “It’s very difficult for me to be objective in terms of how great a threat there is to anybody else.
“But one of the things that drives me and that drives my parents, and many of my friends and family to keep going, is that we don’t want any other family to experience what we have had to experience and, indeed, continue to experience every single day.”
She said a “huge societal change” was needed to stem the rise in anger and hate – including addressing the “frustration” felt by marginalised communities – and it was too easy to blame all problems on the divisions caused by Brexit.
“Brexit didn’t create those problems but it certainly hasn’t helped,” she added.
“It’s exacerbated some of the issues we are facing in our communities up and down the country.
“And you put in the mix of that the anonymity of social media… and I think you have got a toxic cocktail.”
Police, schools and public figures all had a role to play in restoring civility, she argued, but politicians also had a “responsibility” to improve their behaviour.
“That’s why I find it very upsetting when we see some of the scenes we have seen recently in Parliament of bad behaviour across the political spectrum,” she added.