In the late 1940s, when the Nuremberg trials ended, a line was drawn under the subject. To the public who had fought a war against Hitler's Germany, immigrants from eastern Europe to Britain, the United States and the Commonwealth countries were long seen as victims of either Communism, fascism or both, not possible war criminals themselves.
Wladyslaw Dering's case highlighted the unconcern. He was a Pole, and had been a doctor at Auschwitz, helping perform hideous experiments on Jews, but in 1944 obtained false papers and arrived in Britain as a Polish army doctor. He was detained, interrogated by the British, but then freed to practise in London before working for the British colonial administration in Somaliland. He returned to Britain 10 years later to be awarded the OBE, died without facing prosecution, and his past only became known through a libel action.
Britain officially recognised that it might be harbouring war criminals only in 1986, when a list of 17 suspects was handed to Douglas Hurd, the then Home Secretary, by Efraim Zuroff, of the the Nazi-hunting Simon Wiesenthal Centre.
The initial reaction from the then Home Secretary Douglas Hurd was sceptical, but he eventually appointed a commission of inquiry under a former Director of Public Prosecutions, Sir Thomas Hetherington, and William Chalmers, former Crown Agent for Scotland, which has a separate legal system.
A process which the Government probably thought would make the subject go away in fact had the opposite effect. The report concluded: "The cases we have investigated disclose horrific instances of mass murder, and we do not consider that the lapse of time since the offences were committed, or the age of the offenders, provide sufficient reason for taking no action in such cases." Szymon Serafinowicz, the British subject who faced charges of murdering four Jews yesterday, was not one of the cases they considered. Margaret Thatcher examined the evidence herself, and was persuaded.
Eventually, in 1991, a free Commons vote against the opposition of the Lords, passed the War Crimes Act, making it possible to prosecute people for wartime murders abroad, even if they were not British subjects at the time. The Government felt at the time that it would not be fair to deport them to face trial behind what was then the Iron Curtain, to countries that still imposed the death penalty.
Britain was the last Allied country to begin a war crimes trial. Other countries had taken action sooner - the Soviet Union tried thousands, often with perfunctory legal procedures, and in reality for the offence of anti-Communism as much as killing civilians during the war. Adolf Eichmann was captured and tried in Israel in 1960.
The United States has investigated more than 300 suspects, beginning in the the late 1970s, and deported many. France has tried three collaborators in the past decade, Klaus Barbie, Paul Touvier and Rene Bousquet.
One of the most controversial trials was of Jan Demjanjuk, wrongly identified by an Israeli court as a Treblinka guard in the late 1980s and freed in 1993.
Since Britain's late start, members of the Scotland Yard police unit of nine detectives, two historians, two constables and five civilian support staff have visited Russia, the Balkans, the Baltic states, the Ukraine, Latvia, Germany, Poland, Israel, America, Canada and South Africa in their inquiry.
More than 300 cases were reviewed and more than 250 people were cleared. Many suspects have died in the past five years. Of those who have been investigated, only one was under 65.
The war crimes legislation provides for the committal stage of a prosecution to be missed out. The investigating authorities have been careful to keep the identities of suspects secret, to avoid giving grounds for legal arguments that their trials have been prejudiced by publicity.
Papers on six other subjects have been with the Crown Prosecution Service since January. The war crimes unit, in consultation with the CPS, is still investigating 14 other suspects.