The Intriguers Book

Everything is not what it seems…
Neil Mallory, an ex-officer, and paratrooper in the army, is now working behind the scenes. He is James Bond, minus the double o prefix and the license to kill (though he does a pretty good job even without the official sanction).
A French terrorist fraction has absconded with a mini-submarine belonging to the French navy. The sub was originally designed and built by Germany in 1945 but was sunk, with the loss of all hands, shortly after launching. It was consequently raised, salvaged, and recommissioned under the tricolor of France. The L'Alouette is being used to carry out various terrorist operations and her whereabouts while docking is unknown. The Island of St Pierre off the Guernsey coast is a possibility and British Intelligence wants Mallory to investigate.

This has everything you would want and probably expect from a tale of espionage and suspense. Quick and decisive violence, coupled with loads of smoking and drinking (in 1964 when it was published, these were much-desired pastimes and not frowned upon as now fifth-plus years later), and romantic interludes with beautiful, desirable, and willing women. There is virtually something for everyone.
Although in my opinion, this story isn't at the very top of his works, it is a good, solid, and spellbinding yarn and well worth the time and effort to read it.