The British-English noun ploughman’s lunch denotes a meal consisting of bread, cheese, salad and pickle, usually eaten in a pub.

It was invented as a marketing term in 1957 by the Cheese Bureau, an organisation formed to promote the sales of cheese, when it began encouraging pubs to serve this meal.

So far, the word ploughman’s lunch has been first recorded in the Brewers’ Society’s Monthly Bulletin of June 1957, which reported on an event that the Cheese Bureau and the Brewers’ Company jointly organised at Fishmonger’s Hall, London—source: The ploughman’s lunch – guilty or innocent? (16^th July 2007), by Martyn Cornell.

But I have found earlier occurrences of ploughman’s lunch in an account of what appears to be the same event, published in The Birmingham Post and Birmingham Gazette (Birmingham, Warwickshire) of Wednesday 15^th May 1957—the author felt the need to define the word ploughman’s lunch:

London Letter
Light Touch
88, Fleet Street, E.C.4, Tuesday Night

[…]

Cheese and Beer

Into the vast gilded chamber of Fishmongers’ Hall there surged at lunch-time to-day a crowd of dapper City gents looking for—believe it or not—cheese and beer. They found it, and the Lord Mayor, in enormous quantities. From a beer-and-cheese tasting they were supposed to pass to a ploughman’s lunch—more cheese and beer, plus bread and pickles. Where the one ended and the other began nobody could be quite sure.
As a cheese show it was a great success. We were offered Cheddar, Cheshire and Stilton, the “king” of them all, rare blue vinny [= mouldy] from Dorset, round and flat Derby, pungent light red double Gloucester and even fully ripened Dunlop made in Ayrshire. For beer we did still better. Countless brews with names like John Courage, Stingo and Toby ale were flowing, though in glasses mercifully minute since most of us lacked the ploughman’s head, as well as the ploughman’s strength, for dealing with such a flood.
But the main objective was achieved. We came away convinced, as the Cheese Bureau and the Brewers’ Company hoped, that there is much to be said for the old-fashioned pub and ploughman’s lunch—still to be had in the City but only to-day at Fishmongers’ Hall.

I have found another early instance of ploughman’s lunch which confirms that the term, and the meal that it denotes, were invented in order to promote the sales of cheese. It is from Come, Landlord, Fill the Flowing Bowl—in 65 Seconds, an account of the finals of the National Beer Serving Contest, which took place at Preston, published in The Birmingham Post and Birmingham Gazette (Birmingham, Warwickshire) of Wednesday 30^th March 1960—in this case too, the reporter explained what the ploughman’s lunch consisted of:

The contest was organised by the National Trade Development Association a joint organisation of brewers and retailers. It formed part of a meeting arranged by the English Country Cheese Council to launch their “Meet English Cheese” campaign in Preston. There was naturally a great deal of mutual back slapping between beer and cheese.

Eight Varieties

Mr. E. Vanner, a member of the council, said there was “nothing like cheese to promote a thirst or to act as a bit of blotting paper.” He hoped publicans would take to cheese and do away with the sandwiches with curved edges they seem so fond of.
Flushed with success, Mr. Green revealed that he sold eight varieties of cheese at the New Bell.
After seeing half a dozen or so television commercials on cheese; confusing the Dairy Princess with the English Cheese Maiden; eating a “Ploughmans’ [sic] Lunch” (bread and cheese and pickles) and hearing that Mr. John Arlott would be starring in a film on cheese called Mousetrap is Out at the Ritz cinema, it was not with regret that I said goodbye to Preston. And I like cheese.

The Kensington Post (London) of Friday 22^nd September 1961 gave an account of a similar promotional event:

‘Ploughman’s Lunch’ for publicans

Hammersmith grocers and publicans were guests at “Meet English Cheese” meetings at Hammersmith Town Hall last week.
Publicans at an afternoon meeting were entertained to a “Ploughman’s Lunch”—bread, butter, pickles, tomatoes, lettuce, beer and English cheese.
In the evening grocers were guests at a cheese and wine party.
[…]
The campaign, organised by the non-profit making English Country Cheese Council, is aimed at increasing the public’s awareness of the varieties of home-produced cheese.
Before the war only 20 per cent of cheese consumed in this country was home produced. This figure is now 48 per cent.

The following describes one of the places of special interest listed in A Day Out from London, published in The Guardian (Manchester, Lancashire) of Monday 4^th June 1962:

The White Hart, Catsfield, Near Battle, Sussex, is a charming old weather board Sussex Inn. Although lunch is not served, Salads and Ploughman’s Lunch—beer and cheese—are always available.

In 2022, a Twitter storm was caused by the fact that the Tors, a pub in the village of Belstone, in Devon, south-western England, had named its ploughman’s lunch ploughperson’s.

Critics accused the Tors of being ‘woke’ (i.e., alert to injustice and discrimination in society), whereas Dicky Harrison, landlord of the Tors, explained that ploughperson’s was simply meant as a nod to women-farmers.—Cf. Devon pub reaps Twitter storm after adding ploughperson’s to menu, by Steven Morris, published in The Guardian (London and Manchester, England) of Monday 28^th March 2022.