This afternoon’s torrential downpour in London saw me safely ensconced in my library.

With its leather armchair, wood panelling and green shaded lamp, it does look slightly as though it could have been the setting for a scene from a John Buchan novel.

Perhaps with that at the back of my mind I took down a long-neglected copy of Greenmantle, the novel written by Buchan in 1916.

It focuses on a supposed German plan to harness Islamic fundamentalism to sweep the British from the Middle East, India and beyond.

One early passage, where Sir Walter Bullivant is briefing major Richard Hannay, sets the tone and certainly struck a chord with me for its relevance to the modern world.

‘Supposing they had got some tremendous sacred sanction – some holy thing, some book or gospel, or some new prophet from the desert, something which would cast over the whole ugly mechanism of German war the glamour of the old torrential raids that crumpled the Byzantine Empire and shook the walls of Vienna.

‘Islam is a fighting creed and the mullah still stands in the pulpit with the Koran in one hand and a drawn sword in the other.

‘Suppose there is some Ark of the Covenant which will madden the remotest Moslem peasant with dreams of Paradise? What then, my friend?’