The rate of pay growth for British workers has fallen to the lowest level in six months, despite record numbers of people in work across the country, official figures show.

Heaping pressure on the Bank of England to delay raising interest rates from as early as August, the latest snapshot for the British labour market showed the lowest level of unemployment since the mid-1970s was yet to help workers demand higher rates of pay. High rates of employment and low levels of unemployment usually signal rising wages.

The Office for National Statistics said average weekly earnings rose by 2.5% on the year in the three months to May, slowing down from the previous three months when they grew by 2.6%. Pay growth excluding bonuses slowed to 2.7%.

There have been signs of recovery in the British economy that could tempt the Bank to raise interest rates from as early as next month to counter persistently high levels of inflation since the EU referendum two years ago.

Having shuddered to a standstill during the freezing weather earlier this year, the economy rebounded in May thanks to warmer weather and the royal wedding. The Bank has previously said it would raise rates should the economy continue to improve.

The disappointing figures for pay growth came despite unemployment remaining at 4.2%, which was the joint lowest level since May 1975. Lower numbers of people out of work should help workers demand higher pay, but some economists say the creation of low-paid and precarious jobs since the financial crisis has damaged the link between low levels of unemployment and wage growth.

The latest snapshot from the ONS shows the British economy added a further 137,000 jobs, taking the number of people in work to a record high of 32.4 million. Unfilled vacancies stood at a record high of 824,000, amid falls in migration to the UK from the EU after the Brexit vote.

Esther McVey, the secretary of state for work and pensions, said more than 3 million people had entered the workforce since 2010. “The eight-year trend shows the vast majority of roles are in full-time, permanent work that’s higher skilled – which means higher paid too,” she said.

However, the shadow work and pensions secretary, Margaret Greenwood, said millions of workers were “struggling to get by”, while the government was cutting in-work benefits.

The figures from the ONS show real wages are continuing to rise, although only due to falling levels of inflation in recent months. While some economists forecast there will be greater pay rises just around the corner, there are also expectations that inflation will increase as a result of higher petrol prices.

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While the mixed signals from the labour market might deter the Bank from raising interest rates, many economists said Threadneedle Street could still go ahead given stronger economic growth in recent months.

Should the central bank delay, it could create greater levels of Brexit uncertainty ahead of the UK formally leaving the EU next March.

Researchers at the Resolution Foundation said the Bank would need to decide if the poor rate of pay growth was “simply as good as it gets” given the weak growth in the productivity of workers seen across Britain since the 2008 financial crisis.

Stephen Clarke, a senior economic analyst at the thinktank, said: “The news for people once they are in work is less positive, as pay growth continues to disappoint.”