On 31 December 1933, Margetson retired from the
Army, transferring to the Regular Army Reserve of Officers. He joined the
Metropolitan Police, entering directly as a
chief inspector and taking the position of senior administrative officer at No.4 District (South London) headquarters on 1 December 1933. He was later promoted to
Superintendent and took command of "R"
Division (
Blackheath). In August 1936 he was promoted to
Chief Constable and became deputy commander of No.2 District (North London). In February 1938 he was transferred to the same post in No.1 District (West Central London), and in October 1938 to the same post in No.3 District (East London). In February 1940 he was promoted to
Deputy Assistant Commissioner at "A" Department (Operations and Administration) of
Scotland Yard and in August 1940 he was given command of No.1 District. In March 1946 he received the new rank of
commander. In June 1946, he was promoted to Assistant Commissioner "D" (Personnel and Training) and in October he transferred to become Assistant Commissioner "A" (Operations and Administration). In 1950, he applied for the vacant office of Commissioner of the City of London Police. The job went to one of his colleagues,
Arthur Young, who had succeeded him as Assistant Commissioner "D". In 1947 he was made an Officer of the
Venerable Order of Saint John. He was created a
Commander of the Royal Victorian Order (CVO) in the
1948 New Year Honours and raised to Knight Commander (KCVO) in the
1953 Coronation Honours. In 1955 he was promoted to Commander of the Venerable Order of Saint John. He received the
Queen's Police Medal (QPM) for Distinguished Service in the
1956 Queen's Birthday Honours. ==Later life==