The Remain-supporting MP for Rhondda in south Wales posted two photos showing the insult sprayed twice in red letters across the security shutters protecting his office windows.
The Labour MP told The Independent the incident had been reported to the police and said he “presumed” the vandalism was related to anger over Brexit. Mr Bryant also revealed he had received several death threats in recent weeks.
“It’s shocking, but not surprising, I suppose,” he said of the graffiti. “We didn’t used to be a country like this – we used to be a country that respected political differences, but somehow or other we’ve lost that.”
Several MPs shared their support following the attack. “This vile intimidation and abuse is appalling,” said the Change UK spokesman Chuka Umunna, who also praised Mr Bryant for “standing up to it”.
Why anyone thinks calling me names will stop standing up and speaking out for the best interests of the people of the Rhondda I don't know. They underestimate me. pic.twitter.com/EoWuClosPU— Chris Bryant (@RhonddaBryant)May 18, 2019
It comes as police warn that threats made against MPs have reached “unprecedented levels”, including death threats, online abuse, vandalism and harassment in the street.
Intimidation has not been confined to politicians. Last month a series of homes displaying Labour, Liberal Democrat and Green Party posters in Sussex were vandalised in attacks linked to Brexit, with the words “traitors” and “hypocrites” spray painted on exterior walls.
“It’s surprising and very sad to see people expressing their political views in this thuggish and intimidating way,” said Zoe Nicholson, co-chair of the Lewes District Green Party.
“The vandalism is bad enough, but using highly charged language like ‘traitors’ against political opponents is not acceptable.”
Last month Labour MP Helen Goodman’s constituency office windows were smashed in what she suspects may have been an attempt at intimidation over her support for a so-called soft Brexit.
She told The Independent that “in all probability” the incident was motivated by anger at Britain’s failure to leave Europe.
Last month parliament’s joint committee on human rights heard that MPs and peers were experiencing “skyrocketing” levels of abuse over Brexit and other issues.
Former Conservative MP Sarah Wollaston, a member of Change UK, told The Independent she is too afraid to advertise meetings in public because of death threats and intimidation.
Recent months have seen a number of high profile incidents of abuse aimed at MPs, including the pro-Remain MP Anna Soubry who was confronted by “yellow vest” protesters near the House of Commons.
MPs have also been abused by pro-Brexit supporters attending sanctioned protests in the streets outside parliament.
Last month Metropolitan Police commander Adrian Usher called on the government to change “outdated” protest laws, and said officers were struggling to enforce current laws regarding political demonstrations.
“We need to move away from the language of ‘peaceful protest’ to talk about ‘lawful protest’ ... We are absolutely in the business of facilitating lawful protest [but] where protest steps over into being unlawful, whether you consider it peaceful or not is a moot point.”
A spokeswoman for South Wales Police said the force was “investigating a report of criminal damage to the constituency office of Rhondda MP, Chris Bryant”.
She added: “The office on Dunraven Street, Tonypandy, was targeted sometime between 5pm on Friday evening, 17 May, and 7.30am today, Saturday 18 May. A number of enquiries are currently underway, and anyone with any information about the incident is asked to contact 101, quoting occurrence 1900177951.”