Police investigating claims that a man living in a British nursing home is a Nazi war criminal are preparing to examine evidence of his alleged wartime activities.

The move comes as the Home Office admits it is powerless to stop Konrad Kalejs from leaving the country if he wishes.

The Simon Wiesenthal Centre, which brought the allegations to the attention of police in the UK, is sending its dossier on Mr Kalejs to Leicestershire police at their request.

Mr Kalejs, who is currently living in Catthorpe nursing home in Lutterworth, Leicestershire, is alleged to have taken part in the murder of thousands of Jews in his native Latvia during World War II.

A source at the nursing home alleged Mr Kalejs had given the false name of Viktors Kalnis, when he registered as a paying guest at the home.

He is thought to have arrived in the UK 18 months ago after being deported from both the US and Canada.

The Jerusalem-based Simon Wiesenthal Centre, which is dedictated to hunting Holocaust war criminals, said it feared Mr Kalesj may try to leave the UK if faced with prosecution.

A Home Office spokesman confirmed that under present law there was little to stop him leaving.

Police guard

"There is no extradition warrant, no arrest warrant and no court order against him, so, yes, that would mean there is no way we could stop him leaving," he said.

Two uniformed police officers remain at the entrance to Catthorpe Manor.

Home Secretary Jack Straw is under mounting pressure to explain why an alleged Nazi war criminal was allowed into Britain.

Campaigners say he should be sent back to Latvia to face trial.

But there is concern about Latvia's attitude to prosecuting pro-Nazi collaborators.

The Latvian ambassador to the UK, Normans Penker, told BBC Radio 4's Today programme no such prosecutions had taken place in independent Latvia.

He said any legal move would "depend very much on the file we can gather" on Mr Kalejs.

"So far there are not enough charges to allege anything in any of the countries whether in the US, Canada or Australia," said Mr Penker.

A spokesman from the Attorney General's Office, said any decision on prosecution of Mr Kalejs would depend on the police inquiry and whether the CPS recommended further action.

Six months' grace

There is no automatic, international system to flag up individuals who have been deported previously from other countries - unlike in the US, which operates a Watch List system.

The Home Office said an Australian passport holder - after the war, Mr Kalejs became an Australian citizen - on a visit to Britain would be allowed to stay for six months.

On arrival, such a visitor would be asked to declare that there was no reason why he should be refused entry.

Mr Kalejs, now 86, is alleged to have been an officer in the Latvian Auxiliary Security Police, which collaborated with the Nazis in anti-Jewish and anti-gypsy pogroms.

Nazi-hunters say at least 30,000 Jews and other minorities were murdered by the force, led by Viktors Arajs, who was jailed for life in Hamburg in 1979 for war crimes including murder.

Mr Kalejs is also alleged to have worked as a guard at the Salaspils concentration camp near the Latvian capital, Riga, where other murders were committed.

He has always denied the accusations, and says he was a student during the war.

Mr Kalejs moved to Australia after the war, where he obtained citizenship in 1957.

He then moved to the US, but was deported in 1994 after legal action was taken against him.

'Insufficient evidence'

He subsequently moved to Canada, where he lived for three years before an investigation into his past and deportation back to Australia in August 1997.

The focus of much media attention there, he escaped conviction last year when a court considered the evidence against him insufficient.

He is thought to have left the country in July 1998 and moved to England with his common-law wife.

The 1991 War Crimes Act permits prosecution of suspects on charges alleging crimes committed outside of Britain.

The first trial under the Act was held in March this year.

Retired British Rail worker Anthony Sawoniuk was sentenced to life in prison for murdering Jews while serving as a policeman in Nazi-occupied Belarus.