Exclusive: A former senior Home Office official tells Business Insider that Theresa May personally intervened to ensure the controversial "go home or face arrest" immigration vans were "toughened up".

The source rubbishes claims by May's former chief of staff Nick Timothy that May had actually been opposed to their use and that they had been approved without her knowledge.

"The Home Secretary [was] spoken to on holiday in Switzerland and the wording was slightly changed. It had been toughened up slightly."

Labour leader Jeremy Corbyn calls on Theresa May to apologise following Business Insider's story.

Nick Timothy subsequently deleted his Twitter account.

LONDON — Theresa May personally intervened to ensure the language on the Home Office's notorious "go home or face arrest" immigration vans was "toughened up," a former senior Home Office official has told Business Insider.

The prime minister's former chief of staff Nick Timothy wrote in the Telegraph this week that the decision to approve the controversial billboard vans, which were targeted at undocumented migrants in 2013, had been approved while the then Home Secretary was on holiday in Switzerland and that she had actually been opposed to their use.

However, a former senior Home Office official who was involved in the discussions at the time told Business Insider that May had actually spoken to aides about the vans while she was away and insisted that the language on them be "toughened up."

Timothy, who was May's adviser at the time, claimed on Thursday that May had "opposed" the proposals.

"Theresa May was criticised for the notorious "go home or face arrest" vans that were deployed in 2013," Timothy wrote.

"In fact, she blocked the proposal, but it was revived and approved in a communications plan while she was on holiday. She killed off the scheme later that year but by then the damage had been done."

However, the former Home Office source told BI that emails at the time suggest May had actually discussed the vans with her advisers while away.

And not only did she approve the proposals, May also requested that the language of the slogans was "toughened up" before the vans were rolled out.

"A submission had gone to the Home Secretary outlining what was happening with the vans," the source told BI.

"An email came back that said the Home Secretary had been spoken to on holiday in Switzerland and the wording was slightly changed. It had been toughened up slightly."

Asked about Timothy's claims in the Telegraph, the source replied that he was "either being untruthful or forgetful."

Timothy's Twitter account appeared to have been deleted following the publication of this story.

Labour leader Jeremy Corbyn on Friday called on May to apologise for her role in the campaign.

"The revelation Theresa May wanted to "toughen" the message on those hateful Go Home vans points to a nastiness at the heart of Government," Corbyn tweeted.

"This is not what our country is about. The Prime Minister should apologise for authorising this ugly campaign."

Hostile environment

One of the controversial vans, which encouraged illegal immigrants to leave the UK. YouTube / Channel 4 News

Home Office emails seen by Bloomberg also suggest that May was actively behind the project. According to their report, May and her special advisers were sent plans and publicity images for the vans as early as March 2013. The emails suggest that May's then private secretary Matthew Bligh warned that the images were possibly too soft on illegal immigrants.

"The Home Secretary has commented that it is right to advertise enforcement action but we should not be advertising that we will pay people to leave, which is the effect of the proposed advertisements," he wrote, according to Bloomberg.

"Please can officials consider how the material can be revised to get the messaging right and not expose the Agency to criticism for giving taxpayers' money to illegal migrants?"

Nick Timothy, one of Britain's Prime Minister Theresa May's closest advisers arrives on the final day of the annual Conservative Party Conference in Birmingham, Britain, October 5, 2016. REUTERS/Toby Melville Downing Street sources distanced themselves from Timothy's comments on Thursday, endorsing official accounts that May had been aware of the project being approved at the time.

A spokesperson for the Home Office declined to comment when contacted by Business Insider.

The row comes as May comes under fire for her involvement in the Windrush citizens scandal and her wider involvement in creating a so-called "hostile environment" for immigrants in the UK.