Gentleman's Relish is a type of anchovy paste. It is also known as Patum Peperium.
It was created in 1828 by an Englishman called John Osborn. It tastes very strong, very salty and slightly fishy and contains anchovies (minimum 60%), butter, herbs and spices. The exact recipe however has remained a secret and was passed down by word of mouth over the years. Today, only Elsenham Quality Foods in Elsenham, England is licensed to make it.
Gentleman's Relish can also be added to mince for a different-tasting shepherd's pie or to the mixture for fish cakes, potato cakes and croquettes. Alternatively it can be melted into scrambled eggs or be used as a topping for jacket potatoes.
In recent times Patum Peperium became a blog.Fleming mentions Patum Perperium sandwiches (with cucumber) in the Bond canon.