In 1983 he was promoted to Warrant Officer Class One and appointed as Regimental Sergeant Major, 1st Battalion Coldstream Guards based in Caterham and later Hong Kong. In 1986 he returned to London to understudy GSM Alex Dumon and in June 1987 he was appointed as Garrison Segeant Major, HQ London District, a post he held for fifteen years. GSM Mason was awarded the MBE in the Queen's Birthday Honours List in 1991 and awarded the MVO in Queen Elizabeth, The Queen Mother's 100th Birthday Honours List in August 2000. In his final three years he took charge of the Queen's Golden Jubilee, the Queen Mother's 100th Birthday and sadly her Lying in State and Funeral.
During his service, he served in many countries throughout the world, including Germany, Malta, Cyprus, South Yemen, Zimbabwe, Hong Kong, Canada, The Falkland Islands and Northern Ireland. His appearance, his style and integrity are legendary. A true Coldstreamer who served 40 years with his Regiment. He retired as GSM in July 2002 handing over to the responsibility to Billy Mott. he marked his retirement with a lone march past her Majesty the Queen and Prince Philip at Buckingham Palace as part of the Golden Jubilee Celebrations.