The UK’s plans for asylum reform would break international law, according to the UN’s refugee agency.

The United Nations High Commissioner for Refugees (UNHCR) said the Nationality and Borders Bill would “penalise most refugees seeking asylum in the country via damaging and unjustified penalties, creating an asylum model that undermines established international refugee protection rules and practices”.

The body has urged the Government to re-assess parts of the Bill, currently going through Parliament, that would create an “unfair two-tier asylum system and cause unnecessary suffering to asylum-seekers”.

The legislation, already dubbed the “anti-refugee Bill” by campaigners critical of the plans, intends to make it a criminal offence to knowingly arrive in the UK without permission, with the maximum sentence for those entering the country unlawfully rising from six months’ imprisonment to four years.

It means that, for the first time, how someone enters the UK – legally or “illegally” – will have an impact on how their asylum claim progresses and on their status in the UK if that claim is successful.

Convicted people-smugglers could also face life behind bars, up from the current maximum tariff of 14 years, under the proposals.

The stricter rules are part of Home Secretary Priti Patel’s pledge to fix the UK’s “broken asylum system” and have been hailed by the Government as “fundamental reforms” as part of its “fair but firm” new plan for immigration.

Rossella Pagliuchi-Lor, the UNHCR’s UK representative, said: “This Bill would undermine, not promote, the Government’s stated goal of improving protection for those at risk of persecution.

“It seems to be aimed at deterring refugees, but there’s no evidence that would be the result.

“There’s scope for improving the efficiency of the asylum system. We want to support the UK with that and are heartened that the Home Office is working on it.”

Boats used by migrant for Channel crossings
Home Office permanent secretary Matthew Rycroft rejected suggestions from MPs that elements of the Bill would go against the Refugee Convention (PA)

The comments come after an official Home Office assessment of the proposed reforms found there was “limited” evidence this would cut Channel crossings.

The equality impact assessment for the Bill said: “Deploying these measures does advance the legitimate aim of encouraging asylum seekers to claim in the first safe country they reach and not undertaking dangerous journeys facilitated by smugglers to get to the UK, though evidence supporting the effectiveness of this approach is limited.”

On Wednesday the Home Office’s most senior official, permanent secretary Matthew Rycroft, rejected suggestions from MPs that elements of the Bill would go against the Refugee Convention and could risk criminalising Afghans fleeing the Taliban takeover.

There were “safe and legal routes” for Afghans seeking sanctuary in the UK and the plans would not be in the legislation if they were not “compatible with international obligations”, he told the Commons Home Affairs Committee.

Ms Pagliuchi-Lor will set out the UNHCR’s legal analysis of the Bill when she addresses the Commons Bill Committee on Thursday.