Jeremy Corbyn is to unveil plans to create four new bank holidays to celebrate the patron saints of England, Wales, Scotland and Northern Ireland.
The Labour leader wants to give British workers the day off on St George's Day, St David's Day, St Andrew’s Day and St Patrick’s Day.
Mr Corbyn justified the change to The Telegraph by warning that wages in the UK had not returned to pre-2008 financial crash levels.
Labour insiders said the move would help show the party’s patriotic values while helping those worst affected by poor wage growth.
However, critics are likely to pounce on the impact, with previous analysis suggesting bank holidays cost the economy billions of pounds a year.
Mr Corbyn is expected to discuss it on Sunday – St George's Day – when he appears on BBC One’s The Andrew Marr Show.
He told the Telegraph: "For years, Britain's workers haven't had a proper pay rise, with wages for most people still below 2007 levels.
"After seven years of painful austerity, our workers deserve a break – and under a Labour government, they will have the opportunity of four more days off a year.
“The four nations that make up our great country have rarely been more divided due to the damaging and divisive policies of this Conservative Government.
“But where Theresa May divides, Labour will unite our four nations. A Labour government will make St George’s Day – England’s national day and Shakespeare’s birthday – a public holiday, along with St David’s Day, St Andrew’s Day and St Patrick’s Day.”
Some of the days selected are already holidays in individual UK nations, but not across the country as a whole.
Powers to create bank holidays are devolved to the regional parliaments in Scotland, Wales and Northern Ireland, meaning their approval would be needed to bring the changes in.
However Labour figures believe if they won power and demanded the change it would be difficult for opponents to block it.
Britain lags behind other European countries when it comes to the number of bank holidays they enjoy each year, Labour is arguing.
Party figures have attempted to pre-empt criticism over the policy's cost by saying that there are varying estimates for its impact.
A senior Labour source said a boost for the economy could be generated by those workers who go out spending during the holidays, while conceding other estimates said the opposite.
In 2012, the Centre for Economics and Business Research found that each bank holiday costs the UK economy an estimated £2.3 billion a year.
Mr Corbyn said: “These holidays will be a chance for workers to spend time with their families, in their communities and with their friends.
“But they will also be a chance to celebrate the national cultures of our proud nations in our diversity and mutual respect.
“The next Labour government will give workers the break they deserve and bring our country closer together."
The drive will be seen as an attempt to "own patriotism" after a string of incidents in Mr Corbyn’s early months as leader, including being spotted not singing the national anthem.
The party’s political opponents, especially the Tories and Ukip, are expected to exploit the issue to make gains in Labour heartland seats in the North.
The UK has the lowest number of public holidays among major economies, Labour said – eight compared with a G20 average of 12.
A party source said there was "no reliable measure" for the economic impact of bank holidays which included productivity.