Title: ... With intent to deceive
Description: AKA A Brother for Hugh
From the back cover:

"When his well-meaning, dictatorial father died, James Hyde, who had been a respectful, obedient son for more than fifty years, **wanted** to act like a bird let out of a cage, but he just didn't know how.

Then James's staid path crossed that of an adventurer who offered, in effect, to show him how to live dangerously.  James accepted eagerly, and proved such an apt pupil that, in no time, he had presented the London Metropolitan Police, and the usually cool Tommy Hambledon with an impossible case to solve, and splitting headaches to match."
Subjects: Intelligence service, Intelligence officers, Fiction, British spy stories
Places: Great Britain
Time periods: 1945