After completing his training he was sent to join Col. Wingate's Gideon Force in Ethiopia, where he commanded a mixed group of Ethiopian and Eritrean irregulars (nicknamed "McLean's Foot") against the occupying Italian army.

However, even after he left tension between the partisans and the nationalists in Albania was still causing concern to SOE at which point the Foreign Office and McLean devised a plan to unite them in a common struggle against the Axis forces there.

In April 1944, exactly one year later, McLean returned to Albania with a small team known as "The Musketeers" which included Major David Smiley and Captain Julian Amery.

Early in 1945 McLean volunteered to work for SOE against the Japanese forces in China and was appointed military advisor to Sir Clarmont Skrine, the British consul in Kashgar.

After some years traveling in the late 1940s, McLean resigned his commission and returned to Albania one last time, joining a clandestine organization operated by the United States and British intelligence agencies to undermine Enver Hoxha and the Communist government there.

Coincidentally his new brother-in-law, diplomat Vane Ivanovic, had been a member of the Yugoslav section of the Political Warfare Executive (PWE), the propaganda arm of SOE, during the war.

[7] In the summer of 1952, McLean was chosen as the Unionist Party candidate for Inverness, where the sitting Member of Parliament Lord Malcolm Douglas-Hamilton intended to stand down.

[10] Owing to illness, McLean did not make his maiden speech until March 1956, and he chose to speak about Egypt and Gamal Abdel Nasser whom he regarded with extreme concern.

[14] That year he also began to work with Muhammad al-Badr in resisting Egyptian efforts to install an ally as President of North Yemen where he became the principal military advisor to the Royalist forces.

[15] In June 1964 McLean introduced a Private members bill aimed at protecting some paper mills, shipbuilding and cotton firms which had received government grants from nationalization.

Fielding claimed that he was a kind of "unofficial under-secretary" of the Foreign Office,[17] and quoted a 1979 letter from Harold Macmillan which said "You are one of those people whose services to our dear country are known only to a few".