Detectives from the Metropolitan and City fraud office flew to Vancouver on Saturday after receiving an assurance from Gamil Naguib that he would present himself at the headquarters of the Royal Canadian Mounted Police.
Mr Naguib, 64, who acted as a financier for the charity, agreed to meet Detective Inspector David Crinnion and another officer after failing to turn up for a meeting scheduled for late July in Belgium.
He had been tracked there in March, a month after the Salvation Army issued writs against him and another financier, Stuart Ford, alleging theft of massive sums.
It is understood the detectives want to ask Mr Naguib about his part in a scheme to buy standby letters of credit, banking instruments which can be bought at a discount before their maturity date and sold at a profit later.
The letters were to have been issued by the Panamanian-based Islamic Panamerican Bank, whose stationery describes Mr Naguib as general manager. But the bank does not exist.
One officer said: 'This is a major step in our investigation because we will be able to hear what Mr Naguib has to say for himself. He has said that he can explain everything and, of course, our task is to get at the truth.'
Mr Naguib, a Canadian-Egyptian, was traced to Vancouver after the abortive meeting in Belgium. Canadian mounted police contacted him and asked him to consent to an interview. 'He agreed to come of his own volition,' said the British officer. 'He is expected to be accompanied by his lawyer.'
It is understood officers have traced the disbursement of the money through banks in America, Luxembourg and Belgium, but one said that they did not know where all of it was now. 'Anyway,' he added, 'it is one thing to find it, and another to get it back.' Only about pounds 1m has been recovered so far.
Mr Ford, 41, from Birmingham, has already been interviewed by police. No one has been charged.