From the Oxford Dictionary of National Biography (2004 Online Edition):
Wilfred Dunderdale: Dec 24, 1899 - Nov 13, 1990
Dunderdale, Wilfred Albert (1899–1990), intelligence officer, was born in Russia on 24 December 1899, the son of Richard Albert Dunderdale, a British shipowner, whose vessels traded between Constantinople and the Russian ports on the Black Sea, and his wife, Sophie. He was educated in Russia, at the Gymnasium in Nikolayev, Ukraine, and was studying naval engineering at Petrograd University when the Russian Revolution broke out in 1917. Much of the Russian navy remained in White Russian hands. Dunderdale was contacted by the Royal Navy, who found his great knowledge of the Russian language and the Russian navy invaluable.
At this time Constantinople, where Dunderdale had numerous friends, had been occupied by the allies. On one occasion in 1919 a submarine was being handed over by the allies to the White Russian navy. Dunderdale discovered that the crew were Bolsheviks who intended to murder the tsarist officers together with the liaison officer (himself) as soon as the vessel sailed. The crew was arrested and Dunderdale was appointed MBE in 1920. In the same year he became a sub-lieutenant in the Royal Naval Volunteer Reserve. During this period he was also sent as the British observer and interpreter to accompany the imperial procurator on his investigation into the murder of the Russian imperial family at Yekaterinburg, which had been recaptured by the White Russian army. As a result he remained convinced of the falseness of the pretender Anastasia, who he said was merely the Polish girlfriend of one of the Bolshevik gaolers who had occasionally done some sewing for the tsarina.
The world of Constantinople, from the end of the First World War until Kemal Atatürk deposed Sultan Muhammad in 1922, was one of classical Byzantine intrigue on a grand scale. The only stabilizing factor was the heavy guns of the Royal Navy, which were trained on the centre of the city. Dunderdale was in his element and in 1921 he was recruited by MI6, with whom he remained until 1959. He had found his spiritual home. He always maintained that his first job for MI6 was to pay off, with gold sovereigns, all the foreign members of the sultan's harem and to repatriate them through the good offices of the Royal Navy.
[SNIP] [Rest of the article discusses his life from 1921 until his death in 1990.]
John Bruce Lockhart, rev.
Sources
personal knowledge (1996) · private information (1996) · The Times (16 Nov 1990) · CGPLA Eng. & Wales (1991)
Wealth at death
£199,876—effects in England: probate, 23 April 1991, CGPLA Eng. & Wales
Notice that the author is this article is John Bruce Lockhart, a relative of R. H. Bruce Lockhart, who figures in such books as Nicholas & Alexandra.
Anyway, I hope this information helps somewhat. If the sources for this story are "personal knowledge" and "private information" I imagine the next step might be to attempt to contact Lord Bruce-Lockhart.
**I've modified my post a bit to remove some of the article. Hopefully this will help keep me within fair use rules. If anybody would like the entire article, I will be happy to email it to them individually. Doing that is within fair use.