Leaflets warning “national traitor” MPs “we’re watching you” were made by a UKIP organiser and circulated outside Westminster, HuffPost UK can reveal.

John Wallace, West Sussex county organiser for UKIP, has refused to apologise for producing the A4-sheets, which were distributed on the day of a crunch vote on Theresa May’s Brexit deal, a spokesman admitted. 

The leaflet reads: “We would classify anyone prepared to vote for this agreement as a national traitor, or state enemy – and we’re watching you.”

UKIP denied the leaflets were sanctioned at a national level and said it was “investigating” the matter. 

When asked about the leaflets, Wallace said: “The language displays my frustration at the obvious deliberate deceit and mendacity of our PM and some of her cabinet, who seem happy to condemn this country to decades of EU purgatory, while claiming to be working hand-in-hand with the EU, in order to achieve the opposite.” 

The leaflets used UKIP’s trademark purple and yellow colour scheme, its logo and had a number for people to call to join the party, which is led by Gerard Batten.  

Copies were also sent to homes in Chichester, which is represented by the Tory MP and supporter of May’s deal, Gillian Keegan. 

It comes after a number of MPs and high-profile figures were mobbed by so-called pro-Brexit and pro-Donald Trump campaigners near Westminster in recent weeks.

Tory MP Anna Soubry, who supports remaining in the EU, was followed down the street by one group and faced chants of “Nazi” while she gave an interview to reporters. The Broxtowe MP later revealed one of her staff was also targeted and called a “spineless c***” on his way into work. 

Left-wing campaigner Owen Jones was also subjected to homophobic abuse and spat at after an interview to Sky News on College Green, which is opposite parliament. 

The surge in threats and intimidation comes in the wake of the murder of Labour MP Jo Cox outside of her Yorkshire constituency office by a far-right activist. 

The man convicted of her violent killing, Thomas Muir, was asked his identify in court, to which he replied: “My name is death to traitors, freedom for Britain.” 

A number of people online claimed the leaflets produced by the UKIP organiser could be viewed as inciting hatred. 

The anti-fascist campaigning charity Hope Not Hate, meanwhile, said the language could have “dangerous repercussions”. 

A spokesman said: “UKIP have become increasingly radicalised over the last year and now occupy the same political terrain that the BNP used to hold.

“This vitriolic language is unacceptable and, as we’ve seen in the past, can have dangerous repercussions.”

Speaker John Bercow has previously said that, in light of the clashes outside parliament, he has received assurances from the Metropolitan Police that there are always officers patrolling the parliamentary estate. 

Sussex Police has told HuffPost UK that it has not received any complaints about the leaflets being delivered to homes. 

A spokesman for UKIP said: ”The material in question was not sanctioned by UKIP head office, and as such is not an official communication of the national United Kingdom Independence Party.

“UKIP is investigating the source of this material.”