At some point between the years 1910-1913 five gentlemen, all former pupils of Elizabeth or Victoria colleges met up while serving in the Siam Constabulary. They deeply lamented over the demise of their favourite game at home and decided to commission a trophy to stimulate interest in rugby football in the islands.

Each contributed a supply of local coinage to this end, they next obtained permission of the HM King Rama VI to convert the coinage into a trophy. Not only did the King of Siam give his permission he also instructed his Royal Crown Silversmith to create a unique trophy.

The Siam Cup was brought to Guernsey by Lt. Col. C H Forty in 1920 when he came on leave and was presented to the Guernsey Sporting Club to be put up for competition. Unfortunately at this time no rugby clubs were actually playing the sport in Guernsey or Jersey.

However in 1928, rugby re-commenced as a sport and Forty requested the trophy be released to the GRUFC for inter-club competition. However it was not until 14 March 1935 that the cup was presented in its first inter-insular as originally intended by it's five donors.

The annual competition has continued since then except between 1941-1947 because of the occupation of the Channel Islands by the Germans when it was hidden from the occupying forces. The original trophy was showing signs of age and the clubs now play for a replica trophy produced from a mould by renowned local silversmith Bruce Russell. The original trophy can be viewed at the RFU museum at Twickenham.