Prawn and Avocado

Reach into the Pret chiller at half past twelve, pull a wedge from the rack, and the side window shows pale pink prawns against pale green avocado on malted brown. The slice is cool against the palm, the film is fogged faintly with condensation, the price-bundled bag a few hundred metres of pavement from a Boots or Tesco till. A made-to-order version at a Pret counter is built differently: a ripe avocado is sliced or mashed onto a slice of buttered brown, a half-squeeze of lemon goes over it, the small cold-water prawns are laid on top in a loose layer with a thin smear of mayonnaise underneath or none at all, and the second slice closes the build. The cross-section is two soft cool layers in close conversation.

The pairing logic explains every other choice. A cold-water North Atlantic prawn is small, sweet and faintly briny, and almost completely lean; a ripe Hass avocado is buttery and yielding and almost flavourless on its own. Each carries what the other does not. The prawn supplies the marine sweetness and the savour that an avocado lacks. The avocado supplies the unctuousness and the cool buttery weight that a small lean prawn cannot bring. The bite reads as a single cool, soft, faintly sea-tasting moment because the two are doing complementary jobs rather than running parallel.

The build fails on ripeness before anything else. Avocado underripe is hard and slightly bitter and tastes of nothing past the grass note; the slice reads as cold cellulose against the shellfish. Avocado overripe goes grey, slack and watery within the time it takes the wedge to reach a desk, and the bread floods to a green-brown stain through the crumb. The window for a ripe Hass is narrow, twenty-four hours either side of the day it gives gently under a thumb press at the stem end, and a sandwich cook who does not know how to feel the fruit through the skin produces an inconsistent wedge from day to day. The prawns stay whole rather than chopped because the small snap of cold flesh against a soft fat is the one textural break in a filling that is otherwise all give; chopped, they vanish into the avocado.

Open the chilled triangle at twelve forty-five at an office desk and the smell on the contact air is faintly buttery first, then a clean cool prawn note coming up behind it, with the lemon as a thin lift above both. The slice gives easily on the first chew, the malted note carrying behind the bread. The avocado arrives cool and soft and almost mute on the tongue. Then the prawns land with their small distinct snap inside the soft layer and the marine sweetness reaches the back of the mouth a beat later. The slice is dry along the buttered face and tinted pale green where the avocado found bare crumb. The aftertaste is mineral and clean and the slice is gone in three or four bites.

The ordering grammar runs across the British supermarket and the high-street sandwich bar. "Prawn and avocado" at an M&S, Tesco, Pret, Boots or Sainsbury's chilled cabinet means specifically the two-protein wedge with prawns and avocado on brown, separate on the same shelf from the plain prawn sandwich and from prawn mayonnaise. At a counter sandwich bar the made-to-order build asks the same question the meal-deal shelf already answers: brown or white, mayonnaise yes or no, leaf or no leaf. The wedge is one of half a dozen prawn sandwiches on the British shelf at any one time, and the customer who reaches for this one consistently is choosing the soft-fat partner reading rather than the bound or the bare one.

The variants and the close relatives are several. Prawn and avocado on white instead of malted brown is the lighter retail reading; the addition of a leaf of iceberg or rocket pushes the build toward a salad sandwich; a smear of Marie Rose sauce instead of plain mayonnaise tints the whole build pink and shifts it toward the prawn-cocktail family. The plain prawn-mayonnaise sandwich drops the avocado entirely and binds the shellfish in mayonnaise alone; the prawn-cocktail sandwich adds Marie Rose plus shredded lettuce as a faithful three-part transposition of the starter; the prawn sandwich proper leaves the prawns loose under butter with no bind at all; prawn and Marie Rose leads on the coral sauce instead of the green partner. Each of those is a separate page under its own slug, the avocado-led pairing distinct in carrying its own soft fat rather than a tinted dressing.

The Marks and Spencer chilled cabinet

The British packaged prawn sandwich was invented at the M&S Marble Arch flagship in central London in October 1980, a chilled wedge of small cold-water prawns bound in mayonnaise on malted brown, packed inside a hinged plastic triangle. Prawn and avocado appeared on the same chilled cabinet through the 1980s as the chain expanded its sandwich range, the soft buttery fruit partnered with the cold shellfish on the same malted brown, and remained on the M&S shelf through the development of the meal-deal bundle that Boots, Tesco and Sainsbury's built across the late 1990s.

The avocado the sandwich runs on was a 1980s British supermarket arrival. Fresh Hass avocados became widely stocked across British supermarket produce sections only through the late 1970s and 1980s, supplied largely from California and Israel and later from Mexico and Peru, and were a 1980s middle-class fruit by the time M&S put the prawn-and-avocado wedge on the chilled shelf. Pandalus borealis, the small sweet cold-water prawn the build runs on, was being fished out of Norwegian, Icelandic and Greenland waters and shelled at commercial scale by the early 1980s, the same shellfish that supplies the plain prawn mayonnaise wedge.

The trade the wedge belongs to is the British meal-deal sandwich industry, valued at around four billion pounds in annual retail sales by the trade body for British sandwich makers by the mid-2010s. M&S began the chilled-sandwich trial at its Marble Arch flagship in October 1980.