Over 100,000 Britons have expressed interest in hosting Ukrainian refugees, as part of a government programme for households to take in those fleeing Russia's invasion, Prime Minister Boris Johnson said Tuesday.

"It's fantastic that over 100,000 people and organisations have recorded their interest in supporting Ukrainians fleeing the war," he tweeted.

"Thank you to everyone across the country who has stepped up to offer their help so far," he said, less than 24 hours after the launch of the "Homes for Ukraine" programme.

The scheme enables individuals, charities, community groups and businesses to volunteer accommodation for refugees for a minimum of six months.

Johnson has had to defend the UK from criticism over its policy towards those fleeing the violence in Ukraine
Johnson has had to defend the UK from criticism over its policy towards those fleeing the violence in Ukraine AFP / Tolga Akmen

It is open to Ukrainian nationals and their immediate family members and will allow them to live and work in the UK for up to three years and access healthcare, benefits and education.

Hosts, who will be given ?350 ($457, 418 euros) a month, must submit the names of those they wish to sponsor, with NGOs and charities working to identify those most in need.

The UK has faced criticism over its policy towards those fleeing the violence in Ukraine, with places limited to those who already have family in the country.

But Johnson has defended the scheme, insisting last week the country was "absolutely determined to be as generous as we possibly can be".

The scheme contrasts that with the treatment of migrants who cross the Channel on small boats
The scheme contrasts that with the treatment of migrants who cross the Channel on small boats AFP / BEN STANSALL

The government has previously come under fire for its response to the evacuation of Kabul after the Taliban takeover in August last year.

Some 15,000 people were taken out of the Afghan capital but the rushed nature of the evacuation meant thousands of Afghans who had worked with the UK there were left behind.

The UK has meanwhile been under domestic pressure to do more to prevent migrants crossing the Channel on small boats, putting themselves at risk in the busy shipping lane.

Johnson made "taking back control" of the UK's borders a key issue in the successful campaign to take the country out of the European Union. But putting that into practice has proved more problematic.

Record numbers -- more than 28,000 -- crossed last year and, unlike for Ukraine's refugees, finding suitable accommodation has been a problem.

Campaigners have said that because of an over-stretched and under-funded system, many asylum seekers spend months stuck in taxpayer-funded hotels while their applications are processed.