AdamG,

You may find this new book of value, Loyal Enemies British Converts to Islam, 1850-1950, by Jamie Gilham, just published by Hurst.

The publisher's advert says:
A well-researched and extraordinary account of British converts to Islam, ranging from my great-grandfather’s elder brother Henry Stanley, first Muslim peer of the realm, to "Harry" St John Philby, uncritical fan of Ibn Saud and Wahhabism. They all swam resolutely against the tide of public opinion of their day.