Sir Keir Starmer is set to pitch Labour as the party to reverse the UK’s slagging growth rates with a major address to hundreds of business leaders.

The Labour leader and shadow chancellor Rachel Reeves will seek to woo senior company executives and investors at an event in London, with around 400 people scheduled to attend the launch of the party’s plan for business.

Sir Keir, whose party has made considerable strides in reassuring and winning over company bosses and City investors in recent years, promises Labour will “roll up our sleeves and get under the bonnet to fix an unprecedented stagnation in British productivity growth”.

The party is strongly favoured to win the next general election, expected to be held in the second half of the year.

Sir Keir, who will call Labour the “party of businesses”, will set out he expects his party to work with the private sector to grow the UK economy.

“The depth of the changes we’ve made to transform the Labour Party’s relationship with business is something I take immense pride in. Your presence here is a testament to the changes we have made over the past four years,” the Opposition leader will say.

“So, all the hard work that has taken us to this point is a vindication and a recognition of that guiding belief. Not just that Labour could be the party of business, but that Labour should be the party of business, and that now, four years on, Labour is the party of business.

The event in central London will be attended be FTSE 100 chief executives as well as international investors and ambassadors. Tickets for the event sold out in four hours, with hundreds said to be on the waiting list to attend.

Sir Keir will say: “You can’t overstate what the British people have been through in the past 14 years. It’s not just the permanent cycle of crisis, there is something much more fundamentally broken in the way this country creates wealth.

“Fifteen years of lost wage growth and an economy with weak foundations that, even in the calmer moments, can’t provide the security working people need to look forward doesn’t just hold back our potential but also rips up the contract and values that keep a country together.

“It undermines the sense that if you work hard and play by the rules, you will have a chance in Britain and the future will be better for your children.”

Among those expected to be at the gathering of politicians and top executives will be Iceland’s executive chairman Richard Walker, a former Conservative backer and donor who this week switched his support to Labour.

The Tories accused Sir Keir of flip-flopping on the economy, with Chief Secretary to the Treasury Laura Trott saying: “Keir Starmer’s record of making promises and then dropping them when they become inconvenient shows Labour will not provide businesses with the stability and certainty they need to invest.”