The British-English phrases to be past one’s sell-by date, to have passed one’s sell-by date, and variants, mean to be ‘stale’, to be no longer innovative, relevant, or effective.

This phrase refers to the practice introduced in Britain in the early 1970s of stamping perishable goods with the latest date by which they may be sold.

Apparently, the term sell-by date first occurred in Report on the Date Marking of Food (London: Her Majesty’s Stationery Office, 1972), by the Food Standards Committee. On Wednesday 5^th July 1972, several British newspapers gave an account of this report—for example the Liverpool Echo (Liverpool, Lancashire, England):

Manufacturers will be forced by law to date-stamp food if a Government committee’s recommendations are accepted.
Pre-packed foodstuffs will have to carry the date they should be sold by or the date of manufacture.
But it would not be an offence to sell food after the “sell by” date.
The report, by the Food Standards Committee, wants to put pre-packed food into two main groups.
Short-life (perishable or semi-perishable): It should be sold within three months and would be clearly stamped with a “Sell-by . . .” date.
Long-life: It should show the date of manufacture or pre-packing.

A literal use of the phrase to have passed one’s sell-by date occurs, for example, in the following from The Press and Journal (Aberdeen, Aberdeenshire, Scotland) of Thursday 4^th January 1979:

Spare a thought for Mr Harry Greig, general manager (sales and marketing) of Forfar firm Angus Countryside Products Ltd. who make all kinds of meat foods.
ACP’s New Year leftovers are a little more substantial than a mere turkey. They have 14,000 meat pies on their hands and they not know what to do with them.
[…]
They will be given away free but Mr Greig stresses they have to go by Saturday otherwise they will have passed the “sell-by” date and will have to go for pig swill.

These are, in chronological order, the earliest figurative uses that I have found of the phrases to be past one’s sell-by date, to have passed one’s sell-by date, and variants:

1 & 2-: From the TV guide, by Tony Pratt, published in the Daily Mirror (London, England):

1-: Of Friday 25^th October 1985:

THE ADVENTURER. Sub-standard thriller series well past its sell-by date.

2-: Of Tuesday 2^nd September 1986:

OPEN ALL HOURS. Past the sell-by date but old episodes of this super series remain a good buy.

3-: From an interview of Martin Clark, an English basketball player, by Robert Pryce, published in The Guardian (London, Manchester and Portsmouth, England) of Monday 15^th December 1986:

“My dream is still to make the NBA,” he says, but, at 25, with a spectacular flaw in his record, he knows he is past his sell-by date.

4-: From A bit on the slide, by Anne de Courcy, about the Women and Humour Exhibition at the Women Artists Slide Library in London, published in The London Evening Standard (London, England) of Monday 9^th March 1987:

Most of the drawings, paintings, collages and cartoons have to do with domestic minutiae, the crumbling interface of the relationship past its sell-by date, the anxieties that flicker through the mind as various social Ides and Nones fall inexorably due.

5-: From Overheard, published in The London Evening Standard (London, England) of Tuesday 17^th March 1987:

A BOTTLE of champagne for any truly overhead remarks we print:
[…]
“She looks well past the sell-by date. . . .”
—Woman at a Clapham party (from Linda Camp).

6-: From The Daily Telegraph (London, England) of Friday 13^th March 1987—as quoted in the Oxford English Dictionary (online edition, March 2021):

Socialism: the package that’s passed its sell-by date.

7-: From Computer Guardian, by Jack Schofield, published in The Guardian (London, Manchester and Portsmouth, England) of Thursday 25^th June 1987:

With the CPC range now creating negligible interest and the Amstrad Spectrum well past its technological “sell by” date, this could be the beginning of the end of the company’s grip on the United Kingdom games market.

8-: From Cat in a basket and on a hot tin roof, by Frederick Harrison, published in The Guardian (London and Manchester, England) of Saturday 8^th August 1987:

A cat on a beach, in or out of a basket, is a guaranteed crowd-puller on the Suffolk coast.
This has put a certain strain upon the ongoing travelling relationship between me and said cat. In ad-speak, Pugs might be described as user friendly, slightly past his sell-by-date, and with bad snack habits . . . which just about sums me up too, now I come to think about it. Whatever: when I arrive back from a snacking binge at some local cafe, I’m likely to find an inevitable little crowd of old ladies gathered around The Beach Basket Cat.

9-: From How the rigid men became flexible friends, an article by Richard Littlejohn about the forthcoming annual conference of the TUC (Trades Union Congress)—published in The London Evening Standard (London, England) of Friday 4^th September 1987:

Yet again there are those within the TUC ready to manufacture yet another divisive confrontation with the representatives of the moderate majority on a point of principle, which has long since passed its sell-by date.

10-: From the review by Nancy Banks-Smith of East Side Story, a BBC documentary about the Isle of Dogs, in East London, published in The Guardian (London and Manchester, England) of Friday 4^th December 1987:

The film was about two 26-year-old men who live on the island. Terry was born there, Anthony Mayhew is a newcomer, a gilt trader, who makes £100,000 “in a good year”. Because of the Stock Market slide, the film was slightly past its sell-by date.

11-: From Television Reviews, by Angela Thomas, published in The Stage and Television Today (London, England) of Thursday 17^th December 1987:

Jim Davidson Comedy Package
Now we know where all the old jokes and wheezes go to die. Thames TV gathers them in and delivers them to South London’s Jim Davidson for a one-hour comedy special.
Young Jim, looking less of a promising juvenile these days, is supposed to be one of the sharper performers on the scene. You would never have known it by the way he trotted out quickie sketches or gags that passed their sell-by date when he was in short trousers.

12-: From the column One Man’s Week, by Alan Cookman, published in the Evening Sentinel (Stoke-on-Trent, Staffordshire, England) of Saturday 19^th December 1987:

MIKE YARWOOD’S Christmas Show was on the box last night. It was pathetic.
You can tell an artist has passed his sell-by date when they squeeze his Yuletide spectacular into the schedules just after August Bank Holiday.