Home Office lawyers told the High Court the Government’s plan to send migrants to Rwanda must not be stopped by legal action, despite warnings the policy is unlawful.

Home Secretary Priti Patel’s department insisted the agreement with the east African nation is in the public interest to deter Channel crossings amid the UN’s refugee agency the UNHCR having reservations about the process.

The first phase of the legal bid to block the plan took place on Friday ahead of the inaugural flight, which is due to take off on Tuesday.

Lawyers brought action on behalf of two migrants due to be on the first flight, alongside the Public and Commercial Services union (PCS), which represents more than 80% of Border Force staff, as well as groups Care4Calais and Detention Action are challenging the policy on behalf of everyone affected.

In written submissions, Home Office lawyers urged the court to reject the application, arguing that it “fails at the first stage”, adding: “The claimants have not identified a serious issue to be tried, still less the strong case they allege for the grant of relief at trial.”

In the court documents, Rory Dunlop QC and Mathew Gullick QC, for the department, said: “The application for interim relief should be dismissed.

“In the alternative, any order for interim relief should be limited.”

They said there was a “strong public interest in permitting these removals to proceed as scheduled” and a “clear public interest in deterring the making of dangerous journeys and the activities of criminal smugglers”.

Raza Husain QC, for the claimants, told the High Court a Home Office document used by the department in the claim was “replete with the suggestion that the UNHCR (the UN refugee agency) has given this plan a green light”.

“Regrettably, the material in this application demonstrates that to be misleading,” he added.

The UNHCR, had a number of concerns about the asylum process in Rwanda, including discriminatory access to asylum, including for LGBT people, a lack of legal representation and interpreters, and difficulties in appealing, the court heard.

Mr Husain said: “These are concerns that have been communicated to the UK authorities and yet the secretary of state’s position … is that the UNHCR has given this plan a green light.

“That is a false claim.”

Laura Dubinsky QC. for UNHCR, which is intervening in the claim, said there had been “inaccuracies” in the way the agency’s views had been described by the Home Office.

She told the court that the agency is concerned about the risk of “serious, irreparable harm” caused to refugees sent to Rwanda, adding the body “in no way endorses the UK-Rwandan arrangement”.

“UNHCR is not involved in the UK-Rwanda arrangement, despite assertions to the contrary made by the Secretary of State,” she later said.

Ms Dubinsky said the agency had “serious concerns about Rwandan capacity”, adding: “UNHCR itself is not in a position to rectify those deficiencies.

“The problems described are deep-rooted structural problems, they are not capable of speedy resolution,” the barrister continued.

She also told the High Court in London that UNHCR has had “a number of meetings” with the Home Office and has said they believe the policy is unlawful.