Mr Kalejs is believed to have arrived in Britain in the summer from Australia, where Jewish groups had demanded his arrest. He was a lieutenant in the notorious Latvian Arajs Kom security force, which operated as a murder squad. He fled from Europe at the end of the war and became an Australian citizen in 1957.
Dr Efraim Zuroff, director of the Israel office of the Simon Wiesenthal Centre, said their investigators tracked Mr Kalejs down to the UK two weeks ago. "Our information is that he is living in the Rugby area," he said. "We are talking about a very, very bad man who should be brought to justice.
"He was a member of a volunteer security force which was responsible for killing tens of thousands of men, women and children, mainly Jews.
"He has been deported from America and Canada for his war crimes and we do not think that the people of Great Britain would welcome him." Dr Zuroff said they were expecting to find out where he was living in the next few days.
Mr Kalejs, who holds an Australian passport, was deported from America in 1994 and was forced to leave Canada two years ago after an immigration inquiry implicated him in the running of a Nazi slave camp near Riga, the Latvian capital.
Mr Kalejs was an officer in the Nazi-affiliated secret police unit and a supervisor at the Salaspils concentration camp in Latvia, where prisoners succumbed to starvation, disease, torture and execution.
Nazi SS murder squads were stretched so thin by the time they arrived in Latvia in 1941, two years into the war, that they recruited local fascists to help. Membership of the unit was voluntary and it was involved in shooting thousands of innocent people during the round-ups.
Dr Zuroff said Mr Kalejs, who has independent wealth, had never been happy in Australia after his return there, especially when his past became known. Mr Kalejs left Australia in June this year. "We will be writing to Warwickshire police to ask them to take action against Kalejs. This man is a war criminal and it is their duty to prosecute him."
David Winnick MP, a member of the Commons Select Committee on Home Affairs, said: "I don't know if the allegations are true but certainly there should be an immediate investigation by the police into these alleged war crimes."
Mike O'Brien, a minister at the Home Office, said he would be happy to pass on details of the Kalejs case to the police, who in turn said they would investigate any complaint.