The Scottish Conservative leader, Douglas Ross, has withdrawn his letter of no confidence in Boris Johnson, citing the war in Ukraine and saying it was no time for a change of leadership. Ross, who has been an outspoken critic of the prime minister, had criticised him over lockdown parties in Downing Street. Johnson, along with dozens of staff and officials, is under police investigation for the breaches. But on Thursday Ross said he had withdrawn the letter of no confidence he had sent to the party’s 1922 committee chair, Sir Graham Brady. A total of 54 letters are needed to trigger a vote on Johnson’s leadership. Ross’ declaration of no confidence was endorsed by the Conservative group at Holyrood. Signs that relations between Johnson and Ross had begun to thaw began after it was announced that the prime minister would attend the Scottish Conservative conference in Aberdeen on 18 and 19 March. Ross told the BBC that “the middle of an international crisis is not the time to be discussing resignations”, but signalled there would be a time to return to Johnson’s fitness to be prime minister. He added: “There will be a time and place to debate Partygate, but, as even Keir Starmer said at the weekend, we should put that on pause while there is war in Europe. “It’s essential that we all fully support what the UK government is doing. In light of Russia’s appalling actions, the government and prime minister need our backing, and they have mine and the whole Scottish Conservative party.” The SNP’s Westminster leader, Ian Blackford, called it “an utterly humiliating U-turn for Douglas Ross” and said he would now “roll out the carpet for the prime minister at the Scottish Conservative conference and pretend that the no-confidence letter that he submitted with such fanfare never happened”. The Metropolitan police are still examining evidence collected by the Cabinet Office investigation, led by senior civil servant Sue Gray, into lockdown breaches in No 10 and the Cabinet Office. More than 80 questionnaires are understood to have been sent to potential rule-breakers, including the prime minister. Johnson is said to have attended at least six of the gatherings under investigation, one of which took place in his own Downing Street flat. Police are not expected to report for several weeks, after which the Cabinet Office has said Gray will release a full copy of her inquiry, which has been held back while police investigate.