Alan Duncan, a senior Conservative critic of Boris Johnson, resigned from the government in order to test whether the new prime minister commands the confidence of the House of Commons.

Duncan resigned as a Foreign Office minister on Monday before the expected arrival of Johnson at Downing Street, becoming the latest in a string of ministers to pre-emptively quit their jobs in protest at Johnson’s likely direction as prime minister.

He then revealed to the BBC that he had applied for a debate to test whether Johnson could command a majority, but was turned down by the Speaker.

The motion read: “That this house has considered the merits of the newly chosen leader of the Conservative party, and supports his wish to form a government”.

If he had lost a vote of confidence, Johnson’s tenure in government could have been sunk before it began. However, Tory rebels fighting against a no-deal Brexit have indicated they are prepared to give him a “time-limited chance” to steer away from that path before they consider bringing him down.

Labour is backing away from holding its own confidence motion on Johnson’s government this week because anti-Johnson MPs believe it would probably be won by the likely new prime minister and have the effect of boosting his confidence.

The departure of Duncan followed announcements on Sunday by Philip Hammond, the chancellor, and David Gauke, the justice secretary, that they would quit on Wednesday, just before Johnson formally becomes prime minister.

Other cabinet ministers have been tipped to follow, including Rory Stewart, the international development secretary who was also in the Tory leadership race. Duncan’s decision is arguably even less of a surprise given his criticisms of Johnson, with whom he spent two years working at the Foreign Office.

In a letter to Theresa May, which Duncan tweeted a photo of, the MP said he was resigning ahead of the changeover of PM “in order to be free to express my views in advance of you relinquishing office”.

I resigned as Foreign Office minister this morning. Here is my letter to the Prime Minister. pic.twitter.com/1kpt7rHsF0 — Sir Alan Duncan MP (@AlanDuncanMP) July 22, 2019

In the letter, Duncan hailed the work of the Foreign Office, adding: “It is tragic that just when we could have been the dominant intellectual and political force throughout Europe, and beyond, we have had to spend every working day beneath the dark cloud of Brexit.”

The most recent falling out between Duncan and Johnson came this month amid a row over Sir Kim Darroch, the UK ambassador to Washington.

When Johnson pointedly refused to back Darroch after the ambassador was condemned by Donald Trump over leaked UK diplomatic cables critical of the White House – following which Darroch resigned – Duncan accused Johnson of throwing the envoy “under the bus”.

Adding to the awkwardness, Duncan, whose Foreign Office brief covers the Americas, was tasked to answer an urgent Labour question the next day in the Commons on Johnson’s role in the Darroch affair. A series of Tory MPs castigated the likely next prime minister, with Duncan indicating he agreed with them.

Timeline Boris Johnson - three decades of sackings and giving offence Show Fired by the Times after landing a job at the newspaper through his family connections. In an article about the discovery of Edward II’s Rose Palace, Johnson allegedly invented a quote from his godfather, the historian Colin Lucas. Discussed plans to have a tabloid journalist beaten up with his fellow Old Etonian Darius Guppy. Johnson said he would try to obtain personal details of the News of the World journalist Stuart Collier. Guppy talked of hiring a contact from south London to assault Collier. In a Telegraph column he predicted that when Tony Blair arrived in Congo “the tribal warriors” would “all break out in watermelon smiles”. He added that the Queen loved the Commonwealth “partly because it supplies her with regular cheering crowds of flag-waving piccaninnies”. It was written the year after he became an MP. Compared same-sex marriage to polygamy and bestiality in his debut book, Friends, Voters, Countrymen. “If gay marriage was OK – and I was uncertain on the issue – then I saw no reason in principle why a union should not be consecrated between three men, as well as two men, or indeed three men and a dog,” said Johnson. Four years before, Johnson described gay men as “tank-topped bumboys” in his Telegraph column. Condemned for publishing an article as editor of the Spectator in which Liverpool fans were blamed for the 1989 Hillsborough disaster. While the article says the event was “undeniably” a tragedy, it added: “That is no excuse for Liverpool’s failure to acknowledge, even to this day, the part played in the disaster by drunken fans at the back of the crowd who mindlessly tried to fight their way into the ground that Saturday afternoon.” It also claimed that people in Liverpool “wallow” in their “victim status”. Fired by the then Tory leader, Michael Howard, from positions as shadow arts minister and party vice-chairman for lying about his extramarital affair with Spectator columnist Petronella Wyatt. When it transpired that tabloid reports, which Johnson had dismissed as an “inverted pyramid of piffle”, were true, he had refused to resign. Suggested that a rise in the number of Malaysian women attending university was down to their desire to find a husband. Suggested the “part-Kenyan” US president Barack Obama had an “ancestral dislike” of the UK. Won “most offensive Erdoğan poem” competition, two months before he was appointed foreign secretary. The limerick, for which he was handed £1,000 by the Spectator, described the Turkish president having sex with a goat. Caught on camera reciting a colonial-era poem by Rudyard Kipling in front of local dignitaries while on an official trip to Myanmar. Johnson, who was accused of “incredible insensitivity”, had been inside the sacred Buddhist site the Shwedagon Pagoda when he began murmuring the first verse of Mandalay, a later verse of which includes the line: “Bloomin’ idol made o’ mud, wot they called the Great Gawd Budd”. Criticised for making incorrect statement that the jailed British-Iranian Nazanin Zaghari-Ratcliffe had been “teaching people journalism” rather than being on holiday in Iran. The then foreign secretary condemned her conviction for spying but his comments were later cited as proof by Iran that she was engaged in “propaganda against the regime”. Came under fire for describing Muslim women in burqas as looking like “bank robbers” and “letter boxes”. Making the comments in his Telegraph column, Johnson also called the garments “oppressive” but added that Britain should not follow other countries in banning them in public. Media firestorm ensued after a neighbour recorded a loud altercation at the home Johnson shared with his partner, Carrie Symonds. Johnson refused to answer questions about the circumstances of the tape, which featured screaming, shouting and banging. A picture of the couple posing happily subsequently appeared in the media, but Johnson repeatedly refused to say who had taken or released the photograph, or whether it was an old picture. The UK's Supreme court rules that the advice prime minister Boris Johnson gave to the Queen over proroguing parliament was "unlawful, void, and of no effect" as it rules that his decision to prorogue parliament was unlawful.

On Sunday, Hammond announced his departure on live TV. Asked on BBC One’s The Andrew Marr Show if he expected to be sacked if Johnson took over, Hammond said: “No, I’m sure I’m not going to be sacked because I’m going to resign before we get to that point. Assuming that Boris Johnson becomes the next prime minister, I understand that his conditions for serving in his government would include accepting a no-deal exit on 31 October and that’s not something that I could ever sign up to.”

Earlier, Gauke told the Sunday Times he would not be able to serve under Johnson if he pursued a no-deal Brexit: “Given that I’ve been in the cabinet since Theresa May came to power, I think the appropriate thing is for me to resign.”

Such resignations have not gone down well with every Tory MP. The former minister Greg Hands tweeted: “In my view, pre-emptive ministerial resignations (if reports are true) in case your own democratically elected party leader is not to your liking are absurd.

“And I say that as a committed Jeremy Hunt supporter. Such moves make a Corbyn government one step more likely.”

While expected, the departure of Duncan will deprive the Foreign Office of an experienced and generally well-liked minister, who was in the role throughout May’s tenure.

The MP for Rutland and Melton since 1992, Duncan has been on the Conservative frontbench for more than 20 years, taking on shadow cabinet briefs including transport as well as trade and industry.