The children and their immediate family members arrived from Poland on Sunday evening and will be assessed before being sent to NHS hospitals to continue their care.

Announcing their arrival, Health Secretary Sajid Javid said: “I am proud that the UK is offering lifesaving medical care to these Ukrainian children, who have been forced out of their home country by the Russian invasion while undergoing medical treatment.”

The Health Secretary told Sky News that six NHS hospitals will provide care for the 21 children and that while they had initially been given six-month visas in order to get them out of the country quickly, these would be extended “to at least three years”.

Mr Javid said once wider family had arrived, there would be 49 people brought to the UK in total.

“I just think it’s great that we can help in this way,” he said.

He said after the three years it would “be up to them to decide what they wish to do”.

Sajid Javid said it had been a “difficult process” to get to the point where Ukrainian refugees could be welcomed to the UK.

Sajid Javid said the Ukraine Family Scheme for refugees was “being made easier and more straightforward” from Tuesday.

He said the Ukraine Family Scheme for refugees was “being made easier and more straightforward” from Tuesday.

The Health Secretary told Times Radio the latest information from Saturday revealed “just over 3,000″ visas had been granted through the programme”.

But he said: “As well as that particular scheme, the extended family scheme being made easier and more straightforward by our online-only process from tomorrow, there’s the new homes for Ukrainian families scheme, which will also go live later this week.”

Mr Javid said there would be a “basic level of security checks” in both schemes, and he said: “I think that is right because you want to get the right balance between sort of speed and the people that we’re trying to help are in a desperate situation, and you want to bring that help as quickly as possible, but also do some basic checks and I think what we have done here is the right balance.”

The Health Secretary had been previously asked whether it had taken too long to get systems in place, but said: “We’re actually one of the first countries to offer humanitarian support, over £400 million of support so far, I think more bilaterally than any other country.

“We’ve offered, we’ve talked about the weapons and the military support.

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“For my part in my department, as well as what we’ve just talked about helping these children, we’ve already sent seven flights of vital medicines, medical equipment, medical supplies, I think I’ve got another one leaving today, which are more in terms of medical supplies in any country.

“So I think collectively we are doing a huge amount as a country.”

The children’s arrival came after a Russian attack on a military training base near Yavoriv in western Ukraine, less than 15 miles (24km) from the border with Poland, a Nato member.

During a call with Ukrainian president Volodymyr Zelensky on Sunday, Mr Johnson “said the UK would continue to pursue more options for bolstering Ukraine’s self-defence, working with partners including at Tuesday’s meeting of the Joint Expeditionary Force (JEF) in London”, a No 10 spokesman said.

Representatives from Denmark, Finland, Estonia, Iceland, Latvia, Lithuania, the Netherlands, Sweden and Norway will attend the summit of the northern European security coalition.

Mr Johnson said Russian president Vladimir Putin’s “barbaric actions” were “testing not just Ukraine but all of humanity”.

Justice Secretary Dominic Raab will travel to The Hague on Monday “to offer Britain’s help in helping to gather the evidence” of potential war crimes committed in Ukraine.

People keen to offer refugees shelter in the UK can register their interest in sponsoring Ukrainians through the Government’s new humanitarian scheme from Monday.

Levelling Up Secretary Michael Gove has said the process of matching Britons with people fleeing the conflict will take place from Friday, while he expects the first refugees to use the new route will make their way to the UK by the end of the week.

Tory MP Danny Kruger told the BBC the scheme would provide Ukrainian refugees with “friends” as well as support.

“When a family arrives, often what they really need is friends. They need people to introduce them to the area, to take them to the church or show them where the playgroup is,” the MP for Devizes said.

“These aren’t services that the local council is always best able to provide, but where there’s a need for professional support – particularly if there’s counselling or training for job opportunity – then we need professional services.”

Meanwhile, the UK will supply Ukraine with more than 500 portable generators to provide energy for essential services, including at hospitals and shelters.

Mr Johnson said they will help ease the power cuts currently crippling the country.

Ukraine conflict: UK offers sanctuary to sick Ukrainian children as refugee scheme expanded after difficult process”