After the war he organised secret operations against the Russians and their allies in Albania and Poland, among other places. Later, as Britain's era of domination in the Arabian peninsula drew to a close, he commanded the Sultan of Oman's armed forces in a highly successful counter-insurgency.

After his assignment in Oman, he organised – with the British intelligence service, MI6 – royalist guerrilla resistance against a Soviet-backed Nasserite regime in Yemen. Smiley's efforts helped force the eventual withdrawal of the Egyptians and their Soviet mentors, paved the way for the emergence of a less anti-Western Yemeni government, and confirmed his reputation as one of Britain's leading post-war military Arabists.

In more conventional style, while commanding the Royal Horse Guards (the Blues), Smiley rode alongside the Queen as commander of her escort at the Coronation in 1953.

During the Second World War he was parachuted four times behind enemy lines. On one occasion he was obliged to escape from Albania in a rowing boat. On another mission, in Japanese-controlled eastern Thailand, he was stretchered for three days through the jungle with severe burns after a booby-trap meant for a senior Japanese officer exploded prematurely.

Though a regular soldier, Smiley was frequently seconded to MI6. As an assistant military attaché in Poland after the war, when the Soviet-controlled Communists were tightening their grip, he was beaten up and expelled as a spy, after an operation he was running had incriminated a member of the politburo.

After that he headed the British side of a secret Anglo-American venture to subvert the newly-installed Communist regime in Albania led by the ruthless Enver Hoxha. But Kim Philby, who was secretly working for the Russians, was the liaison between the British and Americans; almost all the 100 or so agents dropped by parachute or landed by boat were betrayed, and nearly all were tortured and shot. This failure haunted Smiley for the rest of his life.