Home Secretary Jack Straw has ordered an inquiry into the circumstances surrounding the entry of an alleged Nazi war criminal into the UK.

The Home Office said Mr Straw had asked for a "full report" into how Konrad Kalejs, who is under investigation by the police, came to be given permission to enter the UK.

Mr Kalejs, who is living in a Leicestershire residential home, is said to have been joint second-in-command in a Latvian unit which worked with the Nazis in murdering 30,000 Jews during World War II.

Nazi war criminal hunters have alleged that Mr Kalejs, who emigrated to Australia after the war, had been deported from the US and had fled Canada after details about his past emerged.

A Home Office spokesman said: "The home secretary has asked for a full report into the circumstances of how the individual was given permission to be in the country and has asked the immigration service to keep in close contact with the police investigation.

"The home secretary will make any decision necessary in the light of the police investigation."

'Could be arrested'

The inquiry came as pressure mounted from politicians and Jewish groups for Mr Kalejs, 86, to be either deported or prosecuted.

Labour MP David Winnick, a member of the Commons Home Affairs Select Committee, said he had been informed by the Home Office that Mr Kalejs had entered the UK on an Australian passport and his six-month tourist visa runs out on 6 January.

Mr Winnick said: "He could be deported on the grounds that it was not conducive to the public good for him to remain, or, if the Attorney General decides to take action, he could be arrested and charged under the war crimes legislation.

"In view of the very serious allegations made against this person, I believe it would be more appropriate for him to be arrested, if the Attorney General is satisfied there is sufficient evidence to mount a prosecution."

Latvia itself may seek the extradition of Mr Kalejs.

The country's foreign minister, Indulis Berzins, said any action depended on whether Latvia's prosecutor general's office could present relevant evidence.

Lord Janner, chairman of the Holocaust Educational Trust and a former war crimes investigator, called for Mr Kalejs to be prosecuted in this country if there was enough evidence against him.

Otherwise, he said, Mr Kalejs should be deported.

Meanwhile, Leicestershire Police, working in co-operation with specialist officers from Scotland Yard, said they had asked the Simon Wiesenthal Centre in Jerusalem to send witness statements and evidence that implicate Kalejs in mass murder in his native Latvia.

'False name'

A source at Catthorpe Manor, near Catthorpe, where Mr Kalejs is staying, alleged he had given the false name of Viktors Kalnins when he registered as a paying guest at the home.

He said Mr Kalejs had stayed at the home from September 1998 to January this year and had returned again this September.

"He was here last year at about the same time. He stayed about two-and-a-half months and then left again. He then turned up this year at the end of September.

"We were surprised because he was using a different name. He did not use the name of Konrad Kalejs at all."

He said the manor had been bought in 1975 by the Latvian community in Britain for use as a residential home.

It housed exclusively people of Latvian origin, he said, some of whom were funded by social services.