Boris Johnson’s flagship jobs scheme appears to have failed, despite his claim that it helped half a million people into work.

The Way to Work scheme set a target to support 500,000 people into employment by cutting jobseekers’ benefits after four weeks unless they applied for work outside their normal occupation.

Figures from the Office for National Statistics released last week show that the number of unemployed people finding work actually fell by 148,000 compared with the six months before Way to Work began, despite record numbers of job vacancies.

The government is also facing questions about why it set a target of 500,000 when, on average, nearly 1 million unemployed people have found work during similar periods each year since 2001.

On 28 July, the official statistics watchdog challenged the Department for Work and Pensions on why it had not explained how its target was set or measured, a month after the government’s triumphant claims.

Ed Humpherson, director general of the Office for Statistics Regulation, wrote: “There is no clear explanation of how the Way to Work target was defined, how it would be measured, and the methods used to support claims … that the target has been reached.

“It is difficult to attribute and quantify publicly the impact of a campaign like Way to Work in the absence of a clearly defined and published target, and details about how the target will be measured and reported, at the start.

“Measuring government programmes in a robust and transparent way is important, and the statistics/data underpinning any measurement should uphold principles of being trustworthy, of high quality and offer public value. The way the Department has communicated information in this case does not uphold these principles.”

At the end of January, Johnson announced that a “Way to Work drive” would help 500,000 into employment from Universal Credit intensive work search or jobseeker’s allowance, at a time when there were a record 1.2 million vacancies.

Five months later, the DWP tweeted: “We did it!”, and Johnson listed his achievements to the House of Commons on 6 July, the day before he announced his resignation, as including “helping half a million people into work, through the Way to Work scheme”.

Analysis by the Observer of seasonally adjusted figures from the ONS Labour Force Survey shows that 867,310 people moved from unemployment to employment from January to June, with the majority of them finding work before March. In the previous six months, 1,015,954 people moved into work. The average figure for January to June since records began in 2001 is 948,000.

The ONS figures include “people who are not claimants – for instance many married women moving into work – and have no contact with the Jobcentre. Having said that, there is obviously a big overlap [with unemployment benefit claimants],” said Dr David Webster, of the University of Glasgow.

He added that the DWP had never published any data on people getting jobs after being in the Universal Credit intensive work search group, which accounts for most unemployed people.

Way to Work had no separate budget and its central policy change was to cut jobseekers’ benefits within four weeks rather than three months if they were not judged to be trying hard enough to find work by putting themselves forward for jobs outside their normal occupation.

A five-year study published in January suggested that benefit sanctions are counter-productive, and Therese Coffey, the work and pensions secretary, has blocked research assessing their effectiveness – one of many reports on welfare the government has been accused of concealing.

Stephen Timms, Labour chair of the work and pensions select committee, said it would be looking at the figures as part of an inquiry when MPs return in the autumn. “The refusal to set out the evidence behind the claim, unfortunately, is par for the course at the moment,” he said. “We will try and get to the bottom of this in our inquiry on the government’s plan for jobs, which will be starting when parliament returns next month.

“To claim that their policy has been a success seems like business as usual. There might be something more that we’re missing. If there is, they need to tell us what it is.”

The DWP said it would respond in due course to the statistics regulator, and that unemployment had been low, so there were fewer people to find work.

A DWP spokesperson said: “Way to Work successfully supported half a million people into work, helping employers fill the vacancies the economy needed to recover, and lifting incomes as people can be up to £6,000 better off in full-time work than out of work on benefits.

“When there are fewer unemployed people overall in the labour market, the amount of people moving from unemployed to employed is understandably lower. Ahead of the Way to Work campaign, the unemployment rate had fallen to below pre-pandemic levels, meaning 500,000 was a stretching and ambitious target.”