I was going to include a recipe for them but, really, what's the point? You're only going to go and buy a tin of the stuff. And, quite frankly, so am I. In the supermarket, dried marrowfat peas were £1.96/kg. An own label tin of mushy peas was 57p/kg. I went the deluxe route and bought a tin from Harry Ramsden's for 45p. I should declare that I foppishly enlivened the peas with mint, lemon juice and black pepper. This is dangerously close to the other option - a purée, using frozen peas or petit pois. There's a story that a man in Lancashire once served this to a group of family and close friends. I understand he now lives in Bangkok. I include his recipe - serve it at your peril.
I've also included a 'cheat's' recipe for tartare sauce using a good quality bought mayonnaise (which is a long-winded way of saying 'Hellmann's').
The last time I went to a chip shop I had haddock, chips and mushy peas and it cost me £10.50 (I ate in; a takeaway would have been £8.50). The meal was shite - the chips were dry and undercooked and the batter was translucent and flabby. The meal here, including allowances for each and every ingredient (assuming the oil is re-used a few times) cost about £3.50 for one person. And was delicious.