Mushy peas are dried marrowfat peas which are first soaked overnight in water and bicarbonate of soda, and then simmered with a little sugar and salt until they form a thick green lumpy soup. Sometimes mint is used to alter the flavour. Green colouring is often used. This is typically achieved by adding the yellow and blue additives, E102 and E133, which together produce the green effect. The use of artificial colours results in bright green mushy peas. Pure mushy peas, with no colouring, tend to form a more grey-green end product. Sodium bicarbonate is often added to soften the peas to enhance the colour and to inhibit fermentation during soaking, which reduces later flatulence. They are a traditional northern English accompaniment to fish and chips. All over the North they are commonly served as part of the popular snack of pie and peas (akin to the Australian pie floater, but with mushy peas instead of a thick pea soup) and are considered a part of traditional British cuisine. Mushy peas can also be bought in tinned cans. They are also sometimes served in batter as a pea fritter.
On 28 April 2008 the Food Standards Agency asked for a voluntary ban on artificial food colourings and suggested that the ban would be practical by the end of 2009. This would mean that certain foods such as mushy peas, Battenberg cake, Turkish Delight and tinned strawberries might disappear temporarily or permanently.
In North-West England (Cheshire/Merseyside/Lancashire/Greater Manchester areas), they are commonly served with two fried eggs on top as a late night snack.
A Lancashire variant (particularly popular around Bolton and Preston) is parched peas – carlin peas (also known as maple peas, or black peas) are soaked and then boiled slowly and for a long time; the peas are traditionally served with vinegar.