David Frost, who negotiated the Brexit deal on behalf of Boris Johnson, will no longer be given the plum role of national security adviser, the government has announced. Lord Frost’s appointment provoked a backlash from Conservatives including the former prime minister Theresa May because of his lack of relevant expertise. Johnson handpicked Frost to run the Brexit negotiations, replacing the career civil servant Ollie Robbins, who was regarded with suspicion by the Vote Leave veterans in Downing Street. Frost’s pugnacious style and flat rejection of anything more than a bare-bones Canada-style trade deal is regarded as crucial in shaping the eventual agreement. The prime minister gave him a peerage last year. Frost will now take on the role of Brexit and international policy representative – a job that appears to have been created for him. One Whitehall source said Frost’s new post was “the role he wants”. Johnson’s spokesperson rejected the idea that the move meant the prime minister did not trust Frost to be national security adviser, saying that Johnson had been “further considering the responsibilities” of officials following the trade deal with the EU. Labour said the switch in Frost’s role indicated “chaos and confusion” in Number 10. In his new role Frost will continue to work on foreign policy issues, the spokesperson said. He will not, however, have his role directly scrutinised by parliament. Frost is in the unusual position of being both a peer and a government special adviser, and will answer directly to Johnson. He is on leave of absence from the Lords. The prime minister said: “I am hugely grateful to Lord Frost for his herculean efforts in securing a deal with the EU, and I am thrilled that he has agreed to be my representative for Brexit and international policy as we seize the opportunities from our departure from the EU.” Frost said: “I am delighted to take up this new role as the prime minister’s representative on Brexit and international policy. With a new agreement with the EU in place, we have huge opportunities to boost our wealth and define what we stand for as a country internationally, and I very much look forward to supporting the prime minister on this.” The key post of national security adviser will now be filled by Sir Stephen Lovegrove, the permanent secretary of the Ministry of Defence. Lovegrove has a background in the private sector but has also held a series of public sector roles, including chief executive of the Shareholder Executive, the body that managed taxpayers’ holdings in businesses. He was also a board member of the organising committee of the 2012 London Olympics, held when Johnson was mayor of London. Lovegrove is seen by civil service colleagues as a safe pair of hands who helped steer the Ministry of Defence through several crises over the past five years. Former colleagues said he had a strong grasp of the finances and a reliable political antenna, cancelling a personal trip to New York as it became increasingly clear that Gavin Williamson was likely to be sacked by Theresa May as defence secretary following a row about a leak from the national security council. His appointment restores the job to a civil servant – Frost was a political appointee – meaning it will be possible again for the national security director to act as the accounts officer for the £3.2bn intelligence agency budgets, a role that can only be handled by an official. As the MoD’s top official he will have “had oversight of several aspects of the secret state”, according to another former colleague, including the Trident nuclear deterrent, special forces and military intelligence. Downing St said Lovegrove was appointed without a competition. “It wasn’t required. The PM and cabinet secretary identified him as having the right skill set and experience,” a No10 source said. The national security adviser post was previously filled by Sir Mark Sedwill, who was simultaneously the cabinet secretary. When Sedwill took on the double role for May, it raised questions about whether the national security post was being taken seriously enough. May said last year when it was announced Frost would be appointed as national security adviser: “Why is the new national security adviser a political appointee with no proven expertise in national security?”