Boris Johnson has defended the speed of offering refuge to those fleeing Ukraine after he was warned of the danger of schemes turning into “Tinder for sex traffickers”.

The Prime Minister said it was important that “checks both ways” were being carried out before Ukrainian refugees could come to the UK, both to ensure those in need were who they said they were, and also that those offering help were fit to do so.

Appearing in front of the Commons Liaison Committee, Mr Johnson said there had already been cases of “people coming from that war zone who may not be entirely who they say they are” after it was revealed just 2,700 visas have been granted to people wanting to come to the UK under the Homes For Ukraine scheme despite applications reaching 28,300.

The UN refugee agency said four million people have now fled Ukraine since Russia launched its war on February 24.

Meanwhile, a charity which has helped about 70 Ukrainian refugees apply for UK visas said none have been approved in the 13 days since the sponsorship scheme opened.

Volunteers for Love Bristol, which is operating in Poland, said so far everyone they have helped is still waiting for permission to come to the UK.

The PM said he was not going to berate civil servants and officials and “blame people for being slow” as he said they have to “balance some quite difficult objectives”.

Mr Johnson said: “What I wanted was a system that was as light touch as possible and would enable people to come here, but would enable us also to do checks.

“We are outside the Schengen system, we have the advantage of being able to clarify people’s status, (that) they’re bona fide – that’s not a bad thing if you want to have a programme that really works and commands confidence.”

Dame Diana Johnson, the Labour chair of the Home Affairs Committee, told Mr Johnson that some anti-slavery and refugee groups had warned that the Homes for Ukraine sponsorship “risked operating as Tinder for sex traffickers”.

He said: “I think that is one of the reasons why it is important to have as light touch as possible, but to have DBS checks and checks both ways to make sure we have a programme that is really working.”

Defending the rate of progress in resettling refugees, the Prime Minister added: “These numbers are climbing.

“There is no cap on the family reunion scheme, that’s already at the thick end of 25,000. That’s a pretty big town.”

Mr Johnson said he did not yet know how many of the 2,700 people who have been given visas for the Homes for Ukraine sponsorship scheme had arrived in the UK.

He said although many Ukrainians wanted to stay in the region of their country and “in an ideal world” would want to go home, he said “a lot of them increasingly are now wanting to come to other European countries, they’re wanting to come to the UK, and that’s quite right”.

Earlier, refugees minister, Lord Harrington, said progress is starting to be seen thanks to changes the Home Office has made to “streamline” the visa process.

But shadow levelling up secretary, Lisa Nandy, accused the Government of “wasting the amazing generosity that British people have shown”.

The Prime Minister said that while the UK was “certainly looking at going up a gear in our support for the Ukrainians as they defend themselves”, he was not echoing the call of Us President Joe Biden for Vladimir Putin to be removed from office.

Mr Johnson told MPs that “to desire a change of government in itself is not an ignoble thing” as he joked that some MPs on the Liaison Committee would “like a change in this Government”.

But he said: “It’s not the objective of the UK Government and it’s very, very important everybody gets this, we are simply setting out to help to protect the people of Ukraine and to protect them against absolutely barbaric and unreasonable violence.”

It comes as new laws were announced by the Foreign, Commonwealth and Development Office (FCDO) which aim to “prevent Russian oligarch access to UK aviation and maritime technical services”.

The legislation will prohibit the maintenance of aircraft or ships belonging to sanctioned Russian oligarchs or their businesses, the department said.

The FCDO said the new powers, which have been laid in Parliament via a statutory instrument, had been used immediately to sanction Russian businessmen Eugene Shvidler and Oleg Tinkov.

Meanwhile, the finance, trade and shipping sanctions imposed in relation to Crimea have been expanded to the Donetsk and Luhansk regions.

Foreign Secretary, Liz Truss, said: “There is no doubt that (Vladimir) Putin and his elite have been surprised by the strength of our sanctions.

“We will continue to ramp up the pressure so long as Russian troops are in Ukraine, targeting not only the businesses of oligarchs but also their assets and international lifestyles.”

Mr Johnson earlier told MPs that simply agreeing to a ceasefire would not be enough for measures to be lifted, adding that “goes straight into Putin’s playbook”.

Meanwhile, UK defence intelligence analysts reported Russian units are “suffering heavy losses” and have been “forced to return to Belarus and Russia to reorganise and resupply”.