Johnson arrived at London's Gatwick Airport on Saturday morning with his family after breaking off a holiday in the Dominican Republic following Liz Truss's forced resignation as priem minister on Thursday. Broadcaster Sky News photographed the ex-prime minister and his wife Carrie Johnson in economy on an overnight British Airways flight back from the Caribbean with their children and said he received "one or two boos" as he boarded. Johnson later waved to the press gathered outside the VIP exit to the South Terminal as he walked alone to a waiting Range Rover. The flight, which was being tracked by around 7,000 users of the FlightRadar24 website, landed 47 minutes behind schedule. Johnson's allies said he is "up for it" but he is likely to be opposed in the leadership race by his former chancellor Rishi Sunak, whose resignation was key in Johnson's departure from Downing Street this summer, as well as House of Commons Leader Penny Mordaunt. And, while he is yet to formally declare he will run, Johnson's potential reinstatement has divided opinion even among his allies in the parliamentary party, including his former deputy prime minister and foreign secretary Dominic Raab. Appearing on the broadcast round on Saturday, Raab said "we cannot go backwards" and pointed out Johnson still faces a probe into his actions over partygate. He told BBC Radio 4's Today programme: "I stood by Boris, I've got a lot of respect for him. I think he can make a return to frontline politics and I like him personally. "The challenge is this Committee on Privileges and Standards is entering a new phase, there's going to be oral testimony from people from Number 10," Raab continued. "He's going to have to give oral testimony and I just can't see in practice how the new prime minister, in office latest next Friday, could give the country the attention, the focus that it needs and at the same time be giving testimony and be answering all of those questions. So I don't say it with any relish. I'm sad about that situation. We cannot go backwards. We cannot have another episode of the Groundhog Day, of the soap opera of partygate. We must get the country and the government moving forward." Raab backed Sunak, saying he was "very confident" he would stand and had already secured the backing of 100 members of parliament, shoring up sufficient support to be on the ballot for Monday's vote. He told BBC Breakfast: "I think the critical issue here is going to be the economy. Rishi had the right plan in the summer and I think it is the right plan now." Raab said he felt Sunak could "bring the party together with a government of all of the talents." Moments after Johnson landed, former home secretary Priti Patel said she would be backing him but his campaign suffered a blow as former close allies Steve Barclay and Lord Frost urged colleagues to back Sunak. Johnson ally Andrew Stephenson told the Today programme he believed Johnson still had support among the party's membership, some of whom he claimed had wanted the ex-PM on the ballot for the last contest. The Conservative MP and minister said: "There was a huge amount of support from party members still for Boris and they were quite upset that parliamentarians had got rid of him." When asked what had changed, Stephenson said: "Well, clearly what's changed is some of my colleagues who said they had no faith in him and urged him to resign previously, have now gone on record urging him to put his name forward. "There are many more waiting for him to come back and to make a decision on whether he is going to stand but I have heard lots of MPs who now feel that they were rash to judge him before and somewhat rash to encourage him to resign then." Johnson has so far won the support of six Cabinet ministers, including Ben Wallace, Jacob Rees-Mogg, Simon Clarke, Chris Heaton-Harris, Alok Sharma and Anne-Marie Trevelyan. But he was lagging behind in nominations, as was Mordaunt, who became the first to confirm her candidacy. Sunak, who came second against Truss in the last race six weeks ago, has around 87 public declarations, according to a tally by the PA news agency, far ahead of Johnson's 50, while Mordaunt struggles on 18. The Leader of the House, who finished third in the last leadership election, said she had been encouraged by the support she had received from fellow Conservative MPs and wanted to unite the party. She also assured Jeremy Hunt he could stay on as chancellor if she won. Tory MPs will vote on Monday, and two candidates will be put forward to the Tory membership unless one pulls out, with a result being announced on Friday. Candidates have until 2 pm on Monday to secure the 100 nominations, limiting the ballot to a maximum of three candidates. Supporters of Johnson believe that if he can make it to the last two, he will win in the final online ballot of party activists with whom he remains hugely popular. Some MPs have warned they would resign the Tory whip and sit in the Commons as independents if Mr Johnson returns to Downing Street. Analysts at Berenberg Bank said there were greater market risks from a Johnson government, with the Financial Times newspaper reporting the bank told its clients: "Given that a majority of Conservative MPs probably do not want Johnson as their leader, the prospects of mass resignations and a further descent into chaos would loom large."