Lord Pickles wrote in his letter to Mr Dowden: “Mr Johnson has repeatedly been asked by Acoba to clarify his relationship with Merlyn Advisors.
“He has not done so, nor has he denied the reports in the media that he has been working with Merlyn Advisors on a non-contractual basis.”
Government rules state former ministers must not take up new jobs or appointments for two years after leaving public office without advice from Acoba first.
In correspondence dating back to March 18, the watchdog contacted Mr Johnson’s office asking him to set out his relationship with Merlyn Advisors following media reports of his South American visit.
He replied he had no contractual relationship with the company, and in further correspondence said he had not been paid for any meetings in Venezuela.
He added: “I was extensively briefed by HMA [His Majesty’s Ambassador] Caracas before the meeting and used the occasion to push for democracy, human rights and the support of Ukraine.”
Little action can be taken against Mr Johnson
Lord Pickles raised concerns that the trip was paid for by Merlyn Advisers and about the nature of Mr Johnson’s activities for the company, even though he was not under any formal contract.
The peer warned: “If that is the case, there is a reasonable concern that you were acting in a capacity that would be inconsistent with Acoba’s guidance on ‘one-off’ speaking engagements – which does not provide blanket approval for ad-hoc advisory work.”
Mr Johnson did not answer further questions from Lord Pickles about the nature of the meetings or his relationship with Merlyn, and said he believed it was “clearly not necessary to consult or seek Acoba” about the work.
But the watchdog chief disagreed and said there “remains a reasonable concern that you were acting for Merlyn Advisors in a capacity that would be considered advisory work”, which Acoba would have expected him to ask advice for.
He added: “Given the evasive nature of your replies, your failure to answer specific questions put to you, or provide the context of your relationship with Merlyn Advisors, the committee has formed the view that there has been a breach of the Government’s business appointment rules.”
Lord Pickles reported the former prime minister’s actions to Mr Dowden, who is also responsible for overseeing the Cabinet Office, the department that oversees the machinery of Government.
He admitted that little action could be taken against Mr Johnson, as the rules “no longer have relevance in the modern world and are unenforceable to applicants determined to ignore them”.
The Government should reform the rules as it promised in July 2023, Lord Pickles said, to ensure those who breached them would face consequences.
‘This creates serious questions for the Government to answer’
Labour said Acoba’s admonishment of Mr Johnson showed “this rotten Conservative Party simply cannot change”.
Nick Thomas-Symonds, a shadow Cabinet Office minister, said: “Boris Johnson has once again demonstrated a complete disdain for the rules, while Rishi Sunak is too weak to do anything about it. This now creates serious and urgent questions for the Government to answer.
“The rules in place to stop this revolving door are wholly inadequate – and completely toothless, they expose repeated broken government promises to reform the system.
“Only Labour has a plan deliver the change we need. Our ethics and integrity commission will stop the revolving door; we will make the rules enforceable, with proper monitoring and clear sanctions for those who break them.”
A spokesman for Mr Johnson did not wish to comment.