The Home Office says the first interception measures are underway for Rwandan flights

Migrants identified for deportation to Rwanda have been detained, the government said.

Legislation was passed last week to revive a program to send some asylum seekers to the East African country.

The policy seeks to prevent small boats from crossing the canal.

The Home Office did not say how many people had been detained, but it said more operations were expected in the coming weeks.

It said the detentions followed a series of nationwide operations this week.

The announcement came a day before people go to the polls in local elections in England.

The government previously said it was aiming for flights to take off in the spring, but now says it could happen in nine to 11 weeks.

However, the project may still be stalled due to legal challenges.

Anyone the Home Office is considering sending to an African country must give at least seven days' written notice of the intention so they have a chance to respond.

It's unclear whether the detained individuals have received that notification yet — but even if they have, that doesn't mean a flight is imminent, as individuals have the right to launch a legal challenge.

Labor has said it will scrap the Rwanda program if it wins the next election.

However, Ellie Reeves, Labor's deputy national campaign co-ordinator, said no when asked repeatedly if the party would release those detained as part of the policy.

“If their claims fail, we want to return people to their countries of origin, which is why we will set up return agreements and add a thousand caseworkers,” he told BBC Radio 4's World at One programme.

Home Office documents show that 5,700 asylum seekers were identified in the initial group to be sent to Rwanda, but “only 2,143 regularly report to the Home Office and can be detained”.

Number 10 said it was “not accurate” to say the Home Office could not find the others, but a government source admitted it was possible some absconded before they were detained.

Responding to the initial detention, Home Secretary James said wisely: “Our dedicated enforcement teams are working at speed to quickly detain people who have no right to be here, so we can get planes off the ground.”

The teams are trained to ensure detentions are carried out safely, said Eddie Montgomery, director of the Department of the Interior's Office of Enforcement.

He added: “In order to protect the colleagues and detainees involved and to ensure this large-scale operation can be delivered as quickly as possible, it is vital that operational details are kept to a minimum.”

The Home Office said it had increased its detention capacity to more than 2,200 places and had 500 highly trained escorts on standby.

Commercial charters have also been registered and the airport has been put on standby, the department said.

Enver Salomon, chief executive of the Refugee Council, said: “The government's move to detain people is causing fear, distress and great anxiety among men, women and children who have faced war and persecution to reach safety in Britain.”

He said the government should focus on processing asylum claims “efficiently and fairly” rather than “head-on schemes that waste time and resources”.

New figures show 268 people arrived in the UK via the Channel on five boats on Tuesday.

Provisional Home Office figures show a total of 7,567 people traveled between January and April.

This number is 27% higher than the number of visits recorded during the same period last year.

Meanwhile, the first failed asylum seeker has gone to Rwanda under a separate voluntary removal scheme.

Under the scheme, announced in March, migrants whose claims have been rejected will be paid up to £3,000 to travel to the East African country.

Shadow Home Secretary Yvette Cooper called news of the voluntary withdrawal a “pre-election gimmick” and said taxpayers were “paying £3,000 for a volunteer to get on a plane”.

Liberal Democrat leader Sir Ed Davey said: “They had to pay £3,000 to someone. This is doubtless about an election – it's not about seriously stopping the boats.”