Sunak said the government had booked commercial charter planes and trained staff to take migrants to Rwanda, a policy he hopes will boost his Conservative Party's flagging fortunes before an election later this year.

After weeks of opposition in the House of Lords upper house which wants to introduce safeguards to the divisive legislation, Sunak said the government would force parliament to sit late into the night on Monday if necessary to get it passed.

"No ifs, no buts. These flights are going to Rwanda," Sunak told a news conference.

Tens of thousands of migrants - many fleeing wars and poverty in Africa, the Middle East and Asia - have reached Britain in recent years by crossing the English Channel in small boats on risky journeys organised by people-smuggling gangs.

Stopping the flow is a prime goal for the government, but critics say the plan to deport people to Rwanda is inhumane and that the East African country is not a safe place.

Other European countries, including Austria and Germany, are also looking at agreements to process asylum seekers abroad.

LORDS WANT SAFEGUARDS

In Britain, the move has been held up repeatedly by the unelected House of Lords. The legislation is due to return on Monday to the House of Commons - the elected lower house - where lawmakers are expected to remove changes proposed by the Lords and then it will return to the upper chamber.

Some Labour and cross-party peers want the legislation to include safeguards for Afghans who previously helped British troops and to set up a committee to monitor asylum seekers' safety in Rwanda.

Sunak said the government was ready to move fast as soon as the legislation was passed. An airfield was on standby, slots were booked for flights and 500 staff were ready to escort migrants "all the way to Rwanda", he said.

"Plans are in place. And these flights will go, come what may," he said.

Under the policy formulated two years ago, any asylum seeker who arrives illegally in Britain will be sent to Rwanda in a scheme the government says will deter Channel crossings and smash the people smugglers' business model.

Sunak's team hope the pre-election pledge will help turn around his electoral fortunes, particularly among wavering Conservative voters who want to see a reduction in immigration.

He had previously said he hoped the policy would be operational by spring, without giving a precise date.

Polls suggest his Conservative Party will be badly beaten in this year's election by Labour, which has said it will scrap the scheme if it wins power. Labour says it will pursue a deal with the European Union to return some arrivals to mainland Europe.

Even if Sunak is successful in stopping the Lords from blocking the legislation, he may still face legal challenges.

Charities and rights groups say they would try to stop individual deportations and the trade union which represents border force staff is promising to argue the new legislation is unlawful "within days" of the first asylum seekers being informed they will be sent to Rwanda.

"We urgently need the UK government to start treating refugees with decency and stop trying to send them away to an unsafe future in Rwanda," Lucy Gregg, acting head of Advocacy at Freedom from Torture, said in a statement.

"Along with survivors of torture and the support of thousands of caring people up and down the country, we will unite to show airlines that we won't tolerate them flying in the face of human decency."