The round-robin letter of business leaders endorsing one party or another is a relatively new concept in British general elections.

That is because, until around 30 years ago, business leaders were quite happy to nail their colours to the mast publicly.

Big businesses would regularly make donations to political parties – mainly, but not always, the Conservatives – and individual business leaders were always happy to speak up in favour of certain politicians.

This probably reached its zenith in the 1980s when the likes of Sir Rocco Forte, Lord Hanson and P&O’s Lord Sterling were well-known and prominent supporters of Margaret Thatcher.

That Labour had drifted off to the left under Michael Foot made it fairly obvious, in any case, which party was perceived as being best for business.

Things began to change when, under Neil Kinnock’s leadership, Labour began taking a more traditional centre-left position and actively seeking a closer relationship with business.

Ahead of the 1992 general election, Labour threw £500-a-head fund-raising dinners and, although those attending were mainly showbusiness personalities like Stephen Fry, there were also a smattering of business people such as the investment banker Jon Norton, who later married Labour cabinet minister Mo Mowlam.

There was also, under Mr Kinnock’s shadow chancellor John Smith, what became known as the “prawn cocktail offensive” to woo the City.

It was warmly received by the Financial Times, which controversially endorsed Mr Kinnock in 1992, but was easily dismissed by Michael Heseltine, the then deputy prime minister, who scoffed that “never have so many crustaceans died for so little”.

Labour’s efforts to win the support of business intensified when, in 1994, Tony Blair became Labour leader.

A large number of prominent business leaders, including plenty from FTSE-100 companies, subsequently endorsed Labour publicly ahead of the 1997 election.

Early support came from figures such as Chris Haskins, chief executive of Northern Foods; Lord Hollick, chief executive of United News and Media; and Cob Stenham, chief executive of the pulp and paper group Arjo Wiggins.

They were followed in due course by the likes of George Simpson, managing director of GEC; Bob Bauman, chairman of British Aerospace; Robert Ayling, chief executive of British Airways; Niall Fitzgerald, chairman of Unilever; and David Sainsbury, chairman of the supermarket giant.

As valuable were comments from Sir Richard Sykes, chairman of Glaxo – a former donor to the Conservatives – when he told The Guardian in March 1997: “We don’t fear a Labour government at all.”

It was that election, 1997, which saw the first round-robin letter from business leaders endorsing Labour.

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Some 58 top executives signed them in both 1997 and 2001, endorsing Mr Blair.

Although some refused to sign a similar letter ahead of the 2005 election after the Iraq War – among them the Psion founder David Potter and the book retailer Sir Tim Waterstone – Labour still mustered 63 signatures in a letter to the Financial Times, including big names such as Charles Dunstone, the founder of Carphone Warehouse, and Sir Gerry Robinson, the chairman of drinks giant Allied Domecq.

That support, though, had evaporated by the time of the 2010 general election and the less business-friendly Gordon Brown had taken over from Mr Blair.

Not only had Mr Brown introduced a new top rate of income tax of 50p, he had also antagonised business by announcing a 1p increase in both employers’ and employees’ national insurance contributions to be introduced the following spring.

The Conservatives, by now led by David Cameron, successfully weaponised this latter issue in particular.

A letter to The Daily Telegraph, signed by 23 executives, endorsed a pledge to reverse the increase and was signed by leaders of some household names, including Sir Chris Gent, the chairman of GlaxoSmithKline; Simon Wolfson, the chief executive of Next; Justin King, chief executive of Sainsbury; and Sir Stelios Haji-Ioannou, founder of easyJet.

Embarrassingly for Mr Brown, two of the signatories – Sir Stuart Rose, the executive chairman of Marks & Spencer, and Paul Walsh, chief executive of Diageo – were even members of his own Business Council.

This set the trend for the next few years.

A letter containing 103 signatures was mustered for the 2015 election by Lord Feldman, the former Conservative Party chairman, with a number of former Labour supporters – including Sir Charles Dunstone and the theatrical entrepreneur Sir Cameron Mackintosh – among those warning that that “a change in course” under Ed Miliband would “put the recovery at risk”.

Round-robin letters from business leaders were also deployed to rather less successful effect ahead of the Brexit referendum in 2016 and, when Mr Cameron was replaced by Theresa May in the aftermath, the latter was less obviously disposed to business.

There was no such letter ahead of the 2017 election while a subsequent attempt later that year to get top business executives to back the May government’s Brexit strategy in a public letter was, to put it politely, rebuffed.

Similarly, in 2019, given the choice between Boris Johnson – who infamously said “f*** business” in 2018 – and the most anti-business Labour leader ever in Jeremy Corbyn, most executives kept their heads down.

So today’s letter endorsing Labour is something of a throwback to 2010 and 2015 or, further back, to 1997.

The letter, it must be said, does not have quite the star quality of business letters in years gone by.

There are only a handful of genuinely top-rank business leaders of the very recent past on it, such as the former Sky Betting & Gaming chief executive Richard Flint and the former Heathrow chief executive John Holland-Kaye, while the only FTSE-100 company represented on the list is JD Sports, whose chairman Andy Higginson is one of the signatories.

And more than one of the signatories – such as Richard Burge, former chief executive of London Chamber and Commonwealth Enterprise Council – were already members of the Labour Party.

As the Financial Times put it this morning: “Some of the most prominent signatories no longer hold the senior business roles for which they are best known, and the UK’s biggest listed companies have largely avoided signing the letter.”

That said, the very fact that Labour has mustered a letter from business leaders is probably more important than who has signed it.

It shows that the party is being taken seriously by at least some of the business world and that it is taking seriously at least some of the business world’s concerns.

The question now is whether the Conservatives can muster a supportive letter from business leaders themselves this time around. It feels unlikely.