A drink known as a John Collins has existed since the 1860s at the very least and is believed to have originated with a head waiter of that name who worked at Limmer’s Old House in Conduit Street in Mayfair, which was a popular London hotel and coffee house around 1790–1817
45ml (3 parts) Old Tom Gin
30ml (2 parts) freshly squeezed lemon juice
15ml (1 part) sugar syrup
60ml (4 parts) carbonated water to taste
Mix the gin, lemon juice and sugar syrup in a tall glass with ice, top up with soda water, garnish and serve.