LONDON - “Get Brexit done” was the promise, repeated to the point of tedium, that took Boris Johnson’s Conservatives to a landslide victory in Britain’s 2019 election. But four and a half years later, the subject – for so long the defining issue in UK politics – has barely featured in this summer’s campaign.

Keir Starmer, whose Labour party is 20 percentage points ahead on the average of opinion polls, hardly mentions Britain’s relationship with the EU, to the point where he had to deny in a recent interview that he was scared of talking about the issue.

Labour aspires to no significant change in the UK’s status outside the EU, though Starmer said that he was determined to build a “closer, better” relationship with the 27-country bloc, while accusing Johnson of striking “a botched deal” in his haste to exit.

Anand Menon, the director of the thinktank UK in a Changing Europe, said: “If you are so far ahead, whatever you’re doing is working, so why change it?

“There is an underlying nervousness because Starmer is felt to be vulnerable to attack as a former remainer, anti-Brexit, and Labour needs to hold on to pro-Brexit leave voters.”

Although the Brexit referendum took place in June 2016, resulting in a narrow 52% vote in favour of leaving the EU, there was no clear plan for its implementation. That unleashed a period of political turmoil which only ended when Johnson took control of the Conservatives and won the 2019 election.

In the run-up to that vote, Starmer, then the party’s Brexit spokesperson, pressed for Labour to support a second referendum, saying “we would campaign for remain”. But so emphatic was Johnson’s election victory, and so important Labour’s need to win back Conservative votes among Brexit supporters, the topic has been suppressed.

The silence – “Brexit omertà”, as Menon describes it – goes further. The prime minister, Rishi Sunak, is also reluctant to talk about Brexit. This is partly a response to the fact that a diminishing number of Britons believe leaving the EU was a good idea, amid repeated stories emphasising implementation problems.

This week, an Italian trucker said he was kept waiting 55 hours by border officials in Kent while 10 of the plants in his lorry full of vegetation were inspected amid fears they carried harmful pests. Full post-Brexit controls on plant and animal imports were only implemented at the end of April, one of dozens of changes that have affected cross-border businesses.

Meanwhile, the Conservatives have little to point to in terms of Brexit successes. Joe Twyman, founder of polling firm Deltapoll, said: “Last year, when we asked respondents to name any specific benefit of Brexit, only about one in 10 was able to name any specific benefit to the country and only about one in 20 was able to name any specific benefit to them and their family.”

Though Sunak supported Brexit in 2016, he has never been notably enthusiastic, producing a tame video during his campaign to become the leader of the Conservatives in 2022. It featured a man shredding a single sheet of paper marked “EU legislation” and promising weakly to “keep Brexit safe”.

“Sunak did not go into politics to talk about Brexit or immigration and never bought properly into both,” said James Starkie, a member of the main pro-Brexit Leave organisation, and adviser to three Conservative cabinet ministers. “Lots of Conservative policies on both issues have not really come off, and with Labour reluctant to stress either issue, it feels like both parties have made a pact not to talk about either topic.”

Complicating the picture for the Conservatives is Nigel Farage, a rightwing populist actively chasing the party’s votes, who is one of the politicians that does want to talk about Brexit, but only to criticise the government’s record. Farage said at a campaign launch last week that Sunak’s party had presided over “a massive betrayal of the 17.4 million people who voted Brexit”, because it had failed to lead to a sharp fall in immigration.

British voters, however, are focused on the economy, rebranded in the UK as the “cost of living crisis”. The last four and half years of Conservative rule have been dominated by soaring inflation, peaking at 11% in 2022 – levels not seen since the early 1980s – while mortgage costs shot up during the catastrophic 49-day premiership of Liz Truss, Johnson’s successor, after she announced a series of unfunded tax cuts.

Economists estimate that leaving the EU has hit the UK’s gross domestic product, the overall size of its economy, by perhaps between 2% and 3%, but it is not a connection leading politicians are willing to make given that re-entry would almost certainly require another divisive referendum.

Even the UK’s third party, and traditionally its most ardently pro-European, the Liberal Democrats, is barely mentioning Brexit. This week, the party launched its policy manifesto emphasising a promise to invest more in Britain’s health service – a marked contrast to 2019 when it committed to reverse the result of the Brexit vote. The Lib Dems ultimately performed poorly, winning just 11 parliamentary seats out of 650.

Some would like Labour, given it is so far ahead, to be bolder in committing to move closer to the EU.

Tom Baldwin, a former director of communications for the party and anti-Brexit campaigner, pointed to a quieter Labour commitment, made by the party’s spokesperson for foreign affairs, David Lammy. He wants to negotiate a “security pact” with the EU, which could be extended to cover “economic security, climate security”, although it is unclear what it would mean in practice.

But perhaps the most significant issue underpinning the Brexit silence is voter fatigue. Johnson’s victory in 2019 was based partly on sheer exhaustion with an issue that had dominated media coverage for the preceding three years, not least because an election held after the Brexit vote, in 2017, had produced a parliament without a majority for a single party.

“If you do focus groups and mention Brexit, the biggest reaction you get from voters is a yawn and an eye-roll,” said Menon.