Rishi Sunak has raised doubts that asylum flights to Rwanda will take off by the summer, despite official briefings during Suella Braverman’s trip to the African country that plans were on track. During an appearance at the Commons liaison committee, the prime minister told MPs that “no one has promised flights by the summer” after he was pressed over the deterrent effect of the policy so far. However, a Home Office source on the trip earlier this month told reporters “we are certainly working towards getting the flights off before the summer” with several news organisations interpreting that as a pledge to remove people under the scheme. There remain some legal obstacles to the government’s implementation of its deal to detain and swiftly remove all people arriving illegally, with challenges currently going through the courts. In response to questions from home affairs select committee chair, Diana Johnson, Sunak said: “No one has promised flights by the summer. No, that’s not what she [Braverman] said. What we’ve said is that we’ll start flights as soon as we can after legal proceedings have completed. “Ultimately we need to let the legal process play out. It’s only after the legal process has been completed – now people may speculate on when that is likely to happen or not … that we can practically start the flights.” The prime minister had previously indicated he was “confident” the government would fight off any legal challenges to the policy, which have prevented the flights taking off since the first was blocked by the European court of human rights last June. On the visit to Rwanda, Braverman expressed her determination to “move quickly” with deportation flights. “We are working to make this happen as soon as possible. There is every possibility that we can move quickly if we get a good line of judgment in our favour.” However, Home Office sources suggested on Tuesday that the briefings on the trip had merely been setting out a best case scenario should the courts rule in the government’s favour. The Guardian and other news organisations were excluded from the taxpayer-funded visit to promote the government’s plan to deport asylum seekers to the African country, while many rightwing organisations were invited. In December, high court judges found the government’s policy was lawful overall, but quashed the Home Office’s decision to deport a group of people selected for transfer to Rwanda. The court of appeal will hear a challenge to the policy next month before passing judgment in June. If it goes in the government’s favour and backs the original ruling, ministers expect to press ahead with flights immediately. If it goes up to the supreme court, the government is likely to consider whether to start deporting people, with a commitment to return them to the UK if the judgment eventually goes against them. At the hearing, Sunak also argued that children could not be exempted from plans to detain people who cross the Channel in small boats, to prevent the creation of a “pull factor”. He told MPs the controversial policy should include families to prevent an “incentive” for people to bring minors with them. The government has defused a Conservative rebellion from the right of the party for now by agreeing to hold talks with those wanting to toughen up the illegal migration bill. But the prime minister indicated he would not concede ground to more liberal Tories who want to prevent children being detained indefinitely if they arrive in the UK by unauthorised means. Caroline Nokes, the Tory MP who has likened Sunak’s “horrendous” asylum plans to Donald Trump’s “caging of children”, pressed him over the detention of children. The new legislation, which is passing through parliament, has been denounced by the UN refugee agency as in effect an “asylum ban” and been blasted by Labour for its powers to “lock up children”. Also at the committee, Sunak said the HS2 rail link would ultimately finish at Euston, amid questions about the fate of the multibillion-pound infrastructure project. The prime minister said there was nothing “ambiguous” about the final termination point as he confirmed the government still planned to see passengers end their journeys in central London. The levelling up secretary, Michael Gove, raised eyebrows over the weekend when he refused to guarantee that the project would end at Euston. Ministers announced earlier this month that the construction of the Birmingham to Crewe leg of HS2 would be delayed by two years, with the government also “prioritising” initial services between Old Oak Common in west London and Birmingham Curzon Street. It means services will not stop in Euston in central London for years to come.