Suspected war criminal Konrad Kalejs is thought to be planning to fly out of Britain leaving behind a storm of controversy.

Authorities had been urged not to let Latvian Kalejs leave amid claims investigations into his past were incomplete.

Kalejs, 86, is believed to be planning to fly to Australia voluntarily after spending six months at Catthorpe Manor retirement home in Lutterworth, Leicestershire.

If he does leave the country, it means he will avoid deportation proceedings begun by the Home Secretary Jack Straw earlier this week.

Calls for more inquiries were prompted by the claim from the former head of the Australian war crimes unit Robert Greenwood that no "responsible investigative body" there had ever probed the Kalejs case with a view to bringing a prosecution.

Mr Greenwood said his unit had monitored US and Canadian investigations into Kalejs during the late 1980s and 1990s.

But by the time he came to Australia, the war crimes unit had been disbanded.

Files from the former Soviet Union could provide extra evidence against the man and there was no reason why a full probe should not lead to his being charged, he said.

Labour MP Robin Corbett, chairman of the Commons Home Affairs select committee, said this flew in the face of claims that the case had been fully investigated and found wanting by Australian authorities, echoed by the police and Crown Prosecution Service in the UK.

He said Kalejs should be held in this country while a full investigation was carried out to see if a prosecution was possible.

Shadow home secretary Ann Widdecombe said it was not surprising Mr Straw was facing criticism from his own party colleagues and called for him to "bring an end to this farce".

She said: "This episode has been bungled from start to finish."

"Jack Straw is responsible for a situation in which the nation has not even been given a full and proper account of what investigations have taken place and where."

However, Scotland Yard issued a statement saying that the investigation carried out by Australia when Kalejs moved there was "by far the most in-depth and extensive" into his past and included interviews with witnesses in Latvia in the early 1990s.

Hunt for evidence

The senior US investigator who led the probe which resulted in Kalejs's deportation from that country in 1994 also questioned whether there was enough evidence to prosecute him and said deportation from Britain was the best outcome in the circumstances.

Kalejs, who has also been deported from Canada, has denied claims that he was the second in command of a notorious Latvian secret police unit, the Arajs Kommando, responsible for murdering more than 30,000 people, primarily Jews, during the Second World War.

The Australian authorities have pledged to consider any new evidence if he returns to the country.

Later, in a statement clarifying the legal situation, the Home Office insisted there were no powers to detain anyone on behalf of a foreign government without an extradition request.

However, it continued: "The Latvian authorities have been advised that Mr Kalejs is likely to leave Britain very soon, and have been offered information to assist their own inquiries into the case."

The statement stressed no-one could be prevented from leaving the UK if they were not subject to criminal charges, or held if a formal deportation order had not been issued.

"Betrayal of justice"

In Kalejs' case, the Home Office said, he had only been "served with a letter advising him that the Home Secretary is minded to issue" a deportation notice and "inviting him to make representations".

Miss Widdecombe expressed concern that Kalejs was being deported while the police were continuing to investigate his past.

She said it would be a "betrayal of justice and human rights" if new evidence emerged after he had been banished from the country.

Lord Janner, chairman of the Holocaust Educational Trust, said he was "very pleased" the police were still looking into the case.

He was planning to meet David Veness, assistant commissioner at Scotland Yard, to discuss the continuing investigation.

Lord Janner said he would also be meeting Foreign Secretary Robin Cook and the Latvian ambassador in London to discuss whether Kalejs could be extradited to his native land to face trial.

He accepted Mr Straw's position that there was not enough evidence to detain Kalejs in the UK, and admitted that as many of the witnesses to Kalejs's alleged crimes had been murdered, it was difficult to provide evidence.

But he said this was "not the end" of the matter.

"Gesture politics"

However, another trustee of the Holocaust Educational Trust, David Sumberg MEP, said he did not see how the police could have investigated the matter properly in the short time since it emerged Kalejs was in the UK.

And he said the decision to deport him was "gesture politics".

The Simon Wiesenthal Centre in Jerusalem accused Mr Straw of not having the political will to pursue Kalejs and simply "throwing away the hot potato".

Kalejs has been staying at Catthorpe Manor, Lutterworth, since being deported from Canada and the US.