Campaigners in the UK have lost a High Court bid to block the British government's plan to send migrants to Rwanda, paving the way for the first flight to go ahead on Tuesday.

Detention Action said after the ruling: "We will be making an urgent application to the Court of Appeal. This is only the first step in our legal challenge, made stronger by today's evidence."

UK Prime Minister Boris Johnson tweeted: "Welcome news from the High Court today. We cannot allow people traffickers to put lives at risk and our world leading partnership will help break the business model of these ruthless criminals."

Migrants due to be given a one-way ticket to the east African nation - as part of UK Home Secretary Priti Patel's bid to curb Channel crossings - as well as campaign groups and a union, had asked judges to block their upcoming deportation flight.

Up to 130 people had been notified they could be removed.

Priti Patel welcomed the ruling, saying her government will "now continue to deliver on progressing our world-leading Migration Partnership".

She said: "People will continue to try and prevent their relocation through legal challenges and last-minute claims, but we will not be deterred in breaking the deadly people smuggling trade and ultimately saving lives.

"Rwanda is a safe country and has previously been recognised for providing a safe haven for refugees - we will continue preparations for the first flight to Rwanda, alongside the range of other measures intended to reduce small boat crossings."

The London High Court heard 31 people were due on the first flight on Tuesday, with plans to schedule more this year.

Lawyers for almost 100 migrants had submitted legal challenges asking to stay in the UK with the remaining anticipated to follow suit.

The first stage of action was brought by lawyers on behalf of two migrants 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 who are challenging the policy on behalf of everyone affected.

A protester outside the High Commission of Rwanda in London who is against the migrant plan

Mr Justice Swift ruled against the claim and said: "I do not consider that the balance of convivence favours the grant of the generic relief."

"I accept that the fact of removal to Rwanda will be onerous," he added

"It is unlikely that persons transferred would be refused access to the system of asylum. After all, it is the very purpose of the Memorandum of Understanding (for asylum claims to be processed) in Rwanda."

The judge rejected arguments that the agreement between the two countries, known as a Memorandum of Understanding, was "unenforceable", along with other documents that made up the policy.

He said: "They are not legally binding but they are formal documents about arrangements for transfer and how they will be put into practice."

Speaking about the judgment, chief executive of the UK Refugee Council Enver Soloman said that the people involved in this are vulnerable.

He said: "We are disappointed about today's result, and it is extremely worrying that despite these legal challenges and widespread concern, the (UK) government remain determined to press ahead with the removal of people to Rwanda as soon as next week.

"The government are refusing to see the face behind the case. We have already had to directly intervene to stop young people being deported to Rwanda because they were falsely assessed as adults.

"We fear this is a threat to many more young people who are being wrongly held in detention, putting them at great risk.

"These are scared children who are alone, many of whom have undertaken perilous journeys to come to the UK in hope of safety. No one risks their own, or family's, life unless they are running from dangers more acute than they face on these journeys.

"The government must reflect on the initial failures of this plan, and rethink by looking to operating an orderly, humane, and fair asylum system".

UK Home Secretary Priti Patel

UNHCR criticises British plan

Earlier, the UN refugee agency accused Britain of dishonesty over its plan to send asylum-seekers to Rwanda.

The UN agency's lawyer Laura Dubinsky said it "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 told the court.

Ms Dubinsky said the would-be refugees were at risk of "serious, irreparable harm" if sent to Rwanda, and that the UN had "serious concerns about Rwandan capacity".

The UNHCR's concerns include a lack of legal redress in Rwanda and potential discrimination against gay claimants.

"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," the claimants' lawyer Raza Husain said.

"That is a false claim."