A PR director says he has received a death threat that appears to refer to the killing of Jo Cox, following accusations his firm was responsible for “orchestrating” a coup by Labour MPs against party leader Jeremy Corbyn.

Kevin McKeever, a partner at Portland Communications and a former Labour parliamentary candidate, claims to have received a letter warning he will be “coxed”, seemingly a reference to the death of the MP for Batley and Spen who was shot and stabbed in the street outside her constituency surgery in Birstall, West Yorkshire last month.

The alleged threat follows accusations from Unite general secretary Len McCluskey that the PR firm was “critically involved” in Labour MP's attempts to force Mr Corbyn to resign as leader.

Mr McKeever posted a picture of the threat on Facebook and Twitter. It reads: “hello comrade we’ve watched you leave this building we’ve watched you on the strand your blood is the price of your treachery prepare to be coxed :-)”

Mr McCluskey made reference to Portland on Sunday, telling the BBC’s Andrew Marr Show that anti-Corbyn MPs "have been seduced by sinister forces”.

Jo Cox's husband speaks out

He then mentioned "a company called Portland [...] This is a PR company with strong links to Tony Blair, right-wing Labour MPs, who have been critically involved in this orchestrated coup".

Mr McKeever did not initially comment on the allegations, but addressed them after his firm was named in relation by the online blog The Canary.

In pictures: Jeremy Corbyn reshuffle Show all 11 1 /11 In pictures: Jeremy Corbyn reshuffle In pictures: Jeremy Corbyn reshuffle Jonathan Reynolds,Shadow Railways Minister: RESIGNED He resigned as shadow railways minister in protest at the reasons for sacking Pat McFadden In pictures: Jeremy Corbyn reshuffle Kevan Jones, Shadow Defence Minister: RESIGNED He resigned as a shadow defence minister who strongly supports renewal of Trident. Has spoken out against Jeremy Corbyn’s leadership before and was also the centre of a row with Ken Livingstone after he said Jones “might need some psychiatric help” (Jones has previously spoken about his struggle with depression) In pictures: Jeremy Corbyn reshuffle Stephen Doughty, Shadow Foreign Minister: RESIGNED He quit as a shadow foreign minister in protest at the sacking of his colleague Pat McFadden as shadow Europe minister. He said he had “looked at his own conscience” and decided to step down In pictures: Jeremy Corbyn reshuffle Pat McFadden, Shadow Europe Minister: SACKED He was sacked as shadow Europe minister for "disloyalty" to leader Jeremy Corbyn In pictures: Jeremy Corbyn reshuffle Pat Glass, Shadow Europe Minister: SAFE Former junior shadow education minister Pat Glass replaced Pat McFadden as shadow Europe minister In pictures: Jeremy Corbyn reshuffle Emily Thornberry, Shadow Defence Secretary: SAFE She was promoted to shadow defence secretary. She is anti-Trident and therefore more in tune with Corbyn’s stance and replaces Maria Eagle, who was pro-Trident Getty In pictures: Jeremy Corbyn reshuffle Emma Lewell-Buck, Shadow Minister for Devolution and Local Government: SAFE Emma Lewell-Buck was promoted to shadow minister for devolution and local government In pictures: Jeremy Corbyn reshuffle Michael Dugher, Shadow Culture Secretary: SACKED Outspoken critic of Jeremy Corbyn’s leadership, has been sacked as shadow culture secretary for his "incompetence and disloyalty" In pictures: Jeremy Corbyn reshuffle Hilary Benn, Shadow Foreign Secretary: SAFE Hilary Benn remains as shadow foreign secretary, but Corbyn’s team has insisted his role now comes with ‘new conditions’ that he must agree with Corbyn over foreign policy. Benn insists there are no ‘new conditions’ attached to his job and insisted: "I haven't been muzzled. I'm going to be carrying on doing my job exactly as before” In pictures: Jeremy Corbyn reshuffle Maria Eagle, Shadow Culture Secretary: SAFE Maria Eagle, moved from shadow defence to shadow culture secretary as part of Corbyn’s move to make his defence team match his anti-Trident views In pictures: Jeremy Corbyn reshuffle Andy Burnham, Shadow Home Secretary: SAFE Reports linked him to foreign secretary brief, but Corbyn appears to have backed down on sacking Hilary Benn. He does not see eye-to-eye with Corbyn on home affairs such as the Snooper’s charter, but removing your shadow home secretary so soon after starting would have been a dangerous move by Corbyn

Alongside the picture Mr McKeever wrote: “Many of you will have read posts on a blog suggesting a link between me, my workplace and the moves by Labour MPs in Parliament. They have no basis in truth.

“I've made my personal views clear on our party's leadership.

“I have, however, been silent for the past few days due to a hand-delivered death threat, suggesting I should be 'coxed', a reference to the murder two weeks ago of Labour MP, Jo Cox.

“On the advice of the police and in the interests of the personal safety of me, my family, I will not be commenting further.

“We have a Labour Party to return to after this mess. I hope we all reflect.”

Labour MPs have condemned the threat labelling it “disgusting” and “vile”.

Liz Kendall, MP for Leicester West and East Midlands, tweeted: "Disgraceful. Cowardly. And a betrayal of all we stand for. Kevin please know #wearewithyou".

Lucy Powell, who has resigned from the Shadow Cabinet, tweeted: "This is disgusting. This vile (behaviour) has to be stopped."

MP Wes Streeting tweeted: "This is an absolutely disgusting turn of events. Death threats: the new politics? Just grim."