Home Secretary Jack Straw is facing criticism from campaigners over the probable deportation of the suspected Nazi war criminal, Konrad Kalejs.

The Simon Wiesenthal Centre said it is disappointed by the decision not to try Mr Kalejs in the UK for crimes against humanity.

The 86-year-old Latvian born Australian citizen is accused of being a senior officer in a secret police unit that killed 30,000 civilians in Latvia during the Second World War.

Mr Kalejs is facing deportation after the police decided they did not have enough evidence to result in his arrest.

But Nazi hunters say his return to Australia will be a missed opportunity for justice as he is unlikely to face trial once there.

'Terrible' decision

Dr Efraim Zuroff of the Simon Wiesenthal Centre told BBC News Online: "This is terrible because the only chance to bring this man to justice was in Britain or in Latvia.

"If he returns to Australia he will benefit from the country's lax attitude towards Nazi war criminals.

"This is a missed opportunity for the British justice system and I am very upset and disappointed - especially since I just sent the home secretary an appeal urging him to prosecute this man."

Mr Kalejs has already been deported from the US and Canada, leading some to name him the world's least wanted wanted man.

He has been served a formal deportation order by the Home Office, and has seven days to appeal. The Latvian has spent nearly six months in the UK.

Not enough evidence

Mr Straw defended his decision telling the BBC: "We have to follow the rule of law - there is insufficient evidence at this stage to effect an arrest, so no arrest can be made."

Mr Straw added that he believed Mr Kalejs planned to leave the country voluntarily on Thursday but had nonetheless been given notice that the home secretary was "minded" to order his deportation on the grounds that it would benefit the public good.

Specialists from Scotland Yard's now disbanded war crimes unit were understood to have made an assessment of the evidence against the 86-year-old after the allegations against him came to light last week.

Campaigners are 'liars'

Mr Kalejs denies being involved in mass murder and has called his accusers "liars and storytellers".

Lord Janner the former secretary of the Parliamentary War Crimes Group, has welcomed Mr Straw's decision, under the circumstances, saying the home secretary is right to try and have him expelled from the country.

The former war crimes prosecutor, said: "He has already been deported from the United States and Canada and forced out of Australia - he is the most unwanted, wanted man in the world.

"Britain must never become a haven for war criminals and the consequences of this man's actions will follow him wherever he goes."

But the Conservatives have attacked Mr Straw's handling of the issue.

They have called on the home secretary to make a full Commons statement detailing the reasoning behind his decision which they say is inconsistent with his rulings on other high profile cases.