British workers are on course to suffer two decades of lost wage growth, the head of the UK’s trade union movement will say on Tuesday, while warning the government not to attack the right to strike.

Frances O’Grady, speaking in Brighton at the annual gathering of the Trades Union Congress, will accuse the Conservatives of overseeing the “longest squeeze on real wages since Napoleonic times”, with living standards unlikely on current trends to regain their 2008 level until 2028.

Based on official data and recent Bank of England forecasts for inflation and wage growth, the union body calculates the average worker has lost a total of ￡24,000 in real terms since 2008 as a result of pay growth lagging inflation, and is set to lose a further ￡4,000 during the next three years.