Britain will allow 100,000 extra Ukrainians with immediate family in the UK to come to the country in the wake of the Russian invasion.

       Priti Patel also indicated that the new "bespoke humanitarian route" could be widened to cover extended family members including elderly parents.

       But the Home Secretary ruled out any visa-free travel for all Ukrainians because of fears that it could be infiltrated by Russian agents and extremists, leading to another Salisbury-style poisoning in the UK.

       Her proposals came amid a backlash from senior Tory MPs urging her to go further and refugee charities contrasting the UK's "heartless and mean-spirited" offer with the EU's plan to allow Ukrainians to stay for up to three years without any formal asylum process.

       More than 100,000 people a day are expected to flee to Poland from Ukraine, the Polish prime minister said on Monday as Europe faced its biggest refugee crisis since the Second World War.

       Ms Patel told MPs: "Where family members of British nationals do not meet the usual eligibility criteria but pass security checks, UK visas and immigration will give them the permission to enter the UK outside the rules for 12 months and is prioritising all applications."

       She estimated that it would allow an extra 100,000 Ukrainians to seek sanctuary in the UK although it is currently limited to spouses, civil partners, couples living together for over two years and children under 18.

       Government sources said it would "potentially" be widened to extended family members after Ms Patel told Labour's Yvette Cooper, the shadow home secretary, that an elderly parent barred from entering the UK at the weekend would be allowed in under the scheme.

       Sources also did not rule out including Ukrianians without any connection to the UK, but said Britain could and would not "waive visa requirements en masse as some are calling for".

       Ms Patel said security and biometric checks were "a fundamental part of our visa approval process worldwide and will continue", adding: "That is vital to keep British citizens safe and to ensure that we are helping those in genuine need, particularly as Russian troops are now infiltrating Ukraine and merging into Ukrainian forces.

       "Intelligence reports also state the presence of extremist groups and organisations who threaten the region but also our domestic homeland. We know all too well what Putin's Russia is willing to do, even on our soil, as we saw through the Salisbury attack."

       It came as Britain announced new sanctions against Russian banks to heap pressure on Vladimir Putin over his invasion of Ukraine.

       Liz Truss, the Foreign Secretary, said all Russian banks would be hit with a full asset freeze within days as she announced new powers to limit them from clearing payments in sterling, initially targeting Sberbank, Russia's largest bank.

       Grant Shapps, the Transport Secretary, also wrote to all UK ports asking them to ban any Russian flagged, registered, owned, controlled, chartered or operated vessels in advance of laws enforcing it.

       Keir Starmer, the Labour leader, urged ministers to scrap the National Insurance rise because of the knock-on cost of living effect of sanctions.

       Eight former Cabinet ministers including Sir Robert Buckland, Jeremy Hunt, Damian Green and Matt Hancock were among the 38 Tory MPs to put their names to a letter calling for a "flexible and pragmatic approach" to allow Ukrainians to seek temporary refuge in the UK.

       The MPs said: "It is clear that this is not another migration crisis – this is a crisis of war. This should not be business as usual, we need sincere and immediate support for the Ukrainian people. The United Kingdom cannot flag or fail. Our message must be clear: Ukrainian victims of war seeking refuge are welcome.

       Opposition figures criticised Ms Patel's "chaotic" response to the crisis. Ms Cooper said: "The Home Secretary has just said she is announcing a bespoke humanitarian route, but it's extremely unclear from what she's said what the details actually are or who it will apply to."

       Alistair Carmichael, the Liberal Democrat home affairs spokesman, said: "Ukrainians are fleeing for their lives. They deserve far better than just more spin and confusion from our Government. The Home Secretary should come back to Parliament urgently to announce a full refugee scheme to resettle Ukrainians in the UK."

       Enver Solomon, the chief executive of the Refugee Council, said: "I feel the Government is being heartless and mean-spirited and should be going further and rapidly putting in place humanitarian visas so people have a safe route to get here to apply for asylum."