Keir Starmer has written to all of Labour’s general election candidates urging them to mark St George’s Day “with enthusiasm” and to “fly the flag” across the country as he attempts to outmanoeuvre the Tories on national identity.

The Labour leader is trying to reassure swing voters that the party has changed under his leadership after a perceived lack of patriotism under Jeremy Corbyn, who often appeared uncomfortable with British institutions and symbols and argued for a “progressive patriotism”.

However, Starmer told the candidates that “real patriotism” was not just about respecting shared “symbols and sentiments”, but also about serving the country, whether that was through the armed forces, the NHS or as politicians.

Starmer’s shadow cabinet will gather “deep in the English countryside” on Monday for a primarily symbolic meeting at which he will argue that patriotism is a force for good, including in breeding the next generation of sporting talent.

On Sunday, the Labour leader addressed his internal critics in an article for the Sunday Telegraph, telling them that he has “no time” for those who “flinch” at the St George’s flag. He also warned against the flag being surrendered to the far right: “We cannot allow it to become the preserve of the tiny minority who want to drive hatred in our communities.”

Separately, Starmer is facing discontent from Labour MPs over the prominent use of the union flag in election campaign material amid concern that it may alienate ethnic minority voters and others.

Labour insiders have pointed to polling from More In Common in 2019 that found that when people were asked whether seeing the British flag flying made them feel “good” or “bad”, 75% of respondents replied “good”.

A group called “progressive activists” – described by More In Common as being most likely to vote for Labour, the Greens and the SNP – were the only segment in which a majority (69%) replied “bad”, compared with 31% among other respondents.

In his letter, Starmer wrote: “Whether it’s establishing Nato and the NHS as monuments to our collective sacrifice in the 1940s, or the renewal of our public realm at the start of this century, Labour is at its best when it has celebrated, defended and served the values of our country and its people.

“Real patriotism isn’t just about respecting our shared symbols and sentiments. It’s also about serving the country we love. That’s why, after all the changes I have made, this is now a Labour party that will always put country above party.”

In a direct attack on the Tory party, he added: “Now, we know our Conservative opponents, mired in chaos and division, are incapable of saying the same.

“Frankly, when you’ve trashed the economy, hammered mortgage holders, weakened the union, neglected our armed forces, repeatedly broken laws you expected others to follow and denigrated some of our proudest national institutions – from the BBC, to the National Trust and England football team – you lose any right to call yourself a patriotic party.

“No, Labour is the patriotic party now – and we will celebrate St George’s Day with enthusiasm, an enthusiasm shared with each patron saints’ day on our isles … Our changed Labour party is proud of our national identity and ready to serve.”