The first legal action has been launched against Priti Patel’s plan to send asylum seekers to Rwanda as the UN’s refugee agency raised concerns that the UK is “inviting” other European countries to adopt the same divisive immigration policy.

Lodged last Tuesday, the legal challenge states that the home secretary’s proposals run contrary to international law and the UN refugee convention, as well as breaching British data protection law.

Lawyers believe that the Rwanda plans are a “publicity stunt” to discourage people crossing the Channel in small boats. Patel is refusing to disclose key framework documents explaining which migrants may be eligible to be removed.

Larry Bottinick, acting UNHCR representative to Britain, told the Observer: “We are worried that they [the British] are inviting all their European counterparts to do the same. I can understand from their perspective why they would do that – it would give such deals more perceived legitimacy if others do the same.” Denmark has already signalled an interest in outsourcing elements of its asylum system to Rwanda.

Bottinick added that Britain would welcome other countries following suit because it would mean even fewer refugees made it to northern France. He warned: “This would increase the pressures on those states neighbouring conflict areas which are already hosting the great majority of those seeking refuge.”

The action has been launched by the law firm InstaLaw. The Home Office has three weeks to respond and the process could lead to Patel being challenged in the high court. Stuart Luke, partner at InstaLaw, said their case was based on an Iranian asylum seeker who believes he would face an extremely difficult time if sent to Rwanda. “He could be the only Iranian in the country, there’s no network there, no community, no one who speaks the language. How’s he going to manage, survive? How’s he going to find a job, get educated?” said Luke.

Initially the Home Office had given assurances that it would not deport him before 10 May – but on Friday the department backed down and said it was not looking to deport him.

Bottinick said that the UNHCR had “serious concerns” over how the Home Office and Rwanda intended to integrate non-African asylum seekers who formed the vast majority of arrivals in the UK.

“There will be issues as basic as interpretation for Vietnamese and Albanian speakers. The main arrivals to the UK also include Iranians, Iraqis and Syrians. We have serious concerns about Rwanda’s capacity to integrate these groups.”

The legal move came as activists accused Patel of “racist” and “inhumane” policies over the Rwanda plan during her appearance at a Conservative party dinner. The home secretary was speaking at a dinner organised by the Bassetlaw Conservatives in Nottinghamshire on Friday when several activists stood on their chairs and denounced her for the policy.

Footage published on social media shows a woman stand up and tell Patel: “Priti Patel, your racist policies are killing people. Your plans to send people seeking asylum to Rwanda are inhumane and are going to ruin people’s lives.” The woman was booed before being led away. A number of other activists then stood up and made statements.

The Home Office has been contacted for comment.