With the war now over he was granted several periods of home leave, returned home permanently in May 1919, and was demobilised in June. In 1921, he was granted a regular army commission with the Royal Scots Fusiliers as a captain. Beak was in Ireland with his regiment during the Irish War of Independence. In the situation, following the collapse of the British civilian administration, his duties included membership of the "Courts of Enquiry in lieu of Inquests." In July 1921 he is documented as a member of the enquiry into the shooting of Richard and Abraham Pearson by the South Offaly No. 2 Brigade IRA. He was given a brevet promotion to major in 1929, and substantive promotion in 1932, on transfer to the King's Regiment. He was promoted brevet lieutenant colonel in 1935. The substantive promotion followed in 1938, transferring again, this time to the South Lancashire Regiment. During the Second World War, Beak was commander of 12th Brigade, GOC Malta and 151st Infantry Brigade, which he led during Operation Pugilist. General Bernard Montgomery dismissed him from this post after that battle and he never held another command. He was an acting brigadier by 2 August 1940 when his promotion to colonel was gazetted. A Mention in Despatches was gazetted on 20 December 1940, for services between March and June of that year. He was promoted temporary major general in January 1942. He retired from the army on 19 February 1945, retaining the honorary rank of major general. His VC is on display in the Lord Ashcroft Gallery at the Imperial War Museum, London. He is buried in an unmarked grave at Brookwood Cemetery in Surrey but in recognition of his close ties to Cheltenham, where he served as Acting Secretary of Cheltenham YMCA in 1913, they, together with "This England" magazine, erected a commemorative plaque by the main war memorial in the Promenade, which was dedicated by the Mayor of Cheltenham on 27 September 2006.