Jon Thompson said he also had to change the way he travelled after the alarming threats, which were investigated by the Met Police.
They were sent to the HM Revenue & Customs chief executive after he predicted the Brexiteers’ preferred ‘Max Fac’ Irish border option for checking customs would cost businesses between £17 billion and £20 billion a year through additional red tape.
But Mr Thompson vowed not to be silenced from “speaking truth unto power about Brexit”.
The incredible revelation came as he revealed HMRC had only spent a fifth of its No Deal money - despite delays to a new post-Brexit customs system.
He said he had only spent between £50-60 million of the £260 million allocated to HMRC to prepare for a no deal secnario by March.
And he said he’d only employed 2,000 of the extra 4,500 staff he demanded from the Treasury to help prepare for leaving the EU without a deal - because he is expecting Theresa May to strike a deal with Brussels.
The lack of spending and recruitment so far comes despite Mr Thompson admitting the Customs Declaration Service - crucial for processing post-Brexit trade with Europe after Brexit - will be “sub-optimal”. And he said it would take another three years before it was operating fully.
Opening up about the impact of his public warnings on Brexit, Mr Thompson said he found out about his first death threat when his 28-year-old son messaged him saying he was trending on Twitter.
The HMRC boss said it would have been easier to fudge his response when asked about the cost of the proposed ‘Max Fac’ solution to the Irish border question.
“We’ve had to literally change how I travel and what my personal security is and we’ve had two death threats investigation by the Metropolitan Police for speaking truth unto power about Brexit. Those are real situations. I’m still not going to back away from it if I think something’s not going to work - it’s incumbent on me. We live in a democracy so in the end, it’s for governments to decide, ministers to decide what they want to implement but our role as civil servants is to act with integrity and to give them our best advice.
And I think civil servants do do that and I think we’re really rather good at it.
“But in the end it’s a democracy, so you give minister your best advice, you may or may not agree, the minister makes their decision and then that’s government policy, you have to go and implement it as best you can.”