On September 24, Costco's 100g bar was on sale for £4,939.99, when the market price for that much gold was £4,619.70 - equal to a seven per cent mark-up in store. It also had a 50g bar of gold ...

50g and 100g investment-grade bullion bars. Nigel Doolin, Head of Trading at Core Bullion Traders, pictured with one of the Dublin Assay Office gold bullion bars. Picture Conor McCabe Photography.