A Stamp collector from the age of twelve, Marriott was a specialist in Trinidad postal history. In 1952 he sold part of this collection in order to set up a new home after his marriage. He rebuilt his collection again and won medals at international philatelic exhibitions. In 1969, John Wilson, keeper of the Royal Philatelic Collection, suggested Marriott as his successor. As a member since 1965 of the Royal Philatelic Society London's Expert Committee, of which Wilson was Chairman, Marriott was very familiar with the Royal Collection. From 1969 to 1995, he divided his time between Charterhouse and London. His wife replaced him at the boarding house when he was at Buckingham Palace. Because Wilson had preferred to lettime pass between receiving new stamp issues from Britain and the Commonwealth and mounting them into albums, Marriott began to mount the issues of the Elizabeth II's reign into green leather covered albums, and continued the mounting of the King George VI blue collection. Apart from new issues sent by postal administrations, Marriott bought "errors, freaks, and oddities" : stamps with missing colours or inverted picture for example. Like his predecessor, Marriott travelled thirty-nine times with parts of the Collection to international exhibitions. He helped to organize the "London 1980" International Stamp Exhibition at Earl's Court, and the "London 1990" International Stamp Exhibition at Alexandra Palace. He retired from teaching in 1982 and was elected to serve as president of the Royal Philatelic Society London from 1983 until 1986. He had been vice-president of the society since 1979. Facing an increasing amount of work and activities, he was the first keeper of the Royal Collection to have a deputy: Charles Wyndham Goodwyn, president of the RPSL since 1991. He helped Marriott mount the collection, prepare exhibitions and write articles which permitted the Royal Philatelic Collection to be self-sufficient. Marriott gave up his function of keeper to Goodwyn in September 1995.
Tilleard Medal in 1968 from the RPSL for the exhibition of his Trinidad collection. This collection won a gold medal at the 1960 London and the 1967 Amsterdam exhibitions.
