A UK government performance watchdog has slammed the country's interior ministry for its handling of visa applications for Ukrainians fleeing Russia's invasion.

The Parliamentary and Health Service Ombudsman, Rob Behrens, said on Wednesday reports of "chaos and confusion" mirrored complaints it had previously received about the Home Office.

He called for "unnecessary delays and bureaucracy" to be removed, and for the process to be better resourced, made more efficient and transparent.

Ukraine's ambassador to London, Vadym Prystaiko, earlier told a parliamentary committee there had always been "bureaucratic hassles" when applying for a UK visa.

While he got his on time before he took up his post, his wife did not, he told the House of Commons' Home Affairs Committee.

Security checks

Home Secretary Priti Patel and her department have been accused of forcing Ukrainian refugees to jump through hoops to secure visas to travel to the UK.

Hundreds have travelled to the Channel port of Calais in the hope of crossing to join family in the UK, only to have been turned away because of a lack of travel documents.

That has earned it unfavourable comparisons with the European Union, which is allowing Ukrainians without a visa three-year residency rights.

So far, 957 visas have been granted, according to Downing Street.

Prystaiko suggested that with 50,000 to 60,000 Ukrainians in the UK, some 100,000 of their relatives may seek to join them.

London - which made border control a key plank of its successful campaign to leave the EU - insists it needs to carry out proper security checks before issuing visas.

'Horrendous situation'

Behrens said refugees who have fled the fighting "want to be safe and reunited with their family members in the UK as soon as possible".

"It is vital the Home Office acts to correct failings in its handling of visa applications, especially failings we have previously reported and which we are seeing repeated here," he added in a statement.

"In this horrendous situation swift action is needed to make sure the process of getting a visa is simple, accessible and quick. Lives depend on it."

Patel caused confusion earlier this week by insisting an emergency visa application centre had been set up in Calais, only to backtrack and say it was not operational.

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The Home Office then confirmed the centre would be set up 110 kilometres from Calais in Lille. A spokesperson said it will open on Thursday.

The decision to locate it in Lille was "in light of the risks from criminals actively operating in the area around Calais", the spokesperson added.

There was no immediate response from the Home Office to Behrens' criticisms when contacted by AFP.

The Spectator magazine, normally supportive of Prime Minister Boris Johnson's government, this week said the UK was "failing Ukraine's refugees".

It carried a front-page cartoon, headlining it "Border farce".