How 166,000 migrants had been missed by civil service workers who voted to strike after being requested to be at their desks two days per week

The Office for National Statistics (ONS) is facing accusations it is failing to do its job properly after it admitted missing 166,000 migrants who came to Britain in the space of a year – as MPs call for an explanation on concerns over the quality of its data.

Drastic revisions to official data show net migration to the 12 months to June 2023 was 906,000, rather than the 740,000 previously thought – driven by a greater number of immigrants and fewer emigrations than previously thought.

Government statisticians are already being hauled over the coals over the quality of the labour market data they supply to the Bank of England – but workers being told to get back into the office post-Covid are instead electing to strike.

Experts say the relationships between the ONS and the government departments it relies on for statistics appear to be on the wane – potentially spelling trouble for forecasts of everything from the fortunes of our economy to exactly how many people are in the country.

The ONS attributed the radical shift to more complete data and improvements in how it estimates the behaviour of people arriving in the UK from outside the EU.

It uses data from the Home Office, the DWP and its own international passenger surveys to calculate exactly how many people are coming into and leaving the UK on a long-term basis.

It has admitted it missed some people who arrived in the UK from Ukraine as a result of the Russian invasion, and has changed the assumptions it uses for whether someone is moving to the UK permanently.

New data collection on when visas are granted – rather than just when they are used to travel – has also helped them measure migration more accurately. 

Mary Gregory, director of population statistics, said in an official blog that data collection methods had changed as a result of the pandemic because of the switch from surveying migrants to using raw ‘admin data’ to estimate population figures.

‘We’re increasingly confident in our understanding of non-EU migration and we expect revisions for this group to become smaller with time,’ she wrote.

Professor Jonathan Portes of King’s College London, who specialises in studying immigration and labour markets, told the Telegraph something had gone wrong between the ONS and the Home Office, which collects migration figures.

He said the huge revision suggested ‘the communication between the ONS and the Home Office is not as good as it could be,’ adding: ‘There is a significant number of Ukrainians who the Home Office recorded as giving visas to and entering, and the ONS had for whatever reason not counted them in previous statistics.’

The ONS is already under increased scrutiny. A critical independent review of the UK Statistics Authority by former UNESCO statistics boss Professor Denise Lievesley found there was a ‘culture’ problem in getting data from government departments.

Departments were ‘incentivise(d)… to withhold data’ because they saw ‘little to no benefit’ with reporting it. The UKSA oversees the ONS and sister body the Office for Statistics Regulation.

‘As the UK seeks to move away from surveys and rely increasingly on administrative data, resolving these tensions and blockages to data sharing is fundamental and the financial savings could be substantial,’ Professor Lievesley wrote. 

And the stats body is in hot water over the quality of data collected for the Labour Force Survey – a hugely important piece of work that estimates how many people are unemployed across the UK. 

Think tank the Resolution Foundation estimates that almost a million workers are missing from the survey because of issues collecting reliable data for the survey. 

Dame Meg Hillier MP, chair of the Treasury Committee, wrote to the UK’s national statistician Professor Sir Ian Diamond last week to express ‘major concerns’ over the UK’s ability to set good fiscal policy if it doesn’t have reliable data on its workforce.

Bank of England governor Andrew Bailey told the committee earlier this month that due to holes in the Labour Force Survey the Bank does not know ‘whether [we have] a good read or not a good read’ on Britain’s working population.

It prompted Dr Swati Dhingra, who sits on the bank’s rate-setting monetary policy committee (MPC) hit out at the Office for National Statistics (ONS) over inaccuracies in its labour force survey.

At a conference in London she accused the ONS of losing ‘the will to do it as carefully’ as it used to be done. The LFS was suspended in October 2023 over concerns about the accuracy of its data.

The Indian-born economist contrasted the situation with that of her huge native country, saying: ‘There are a billion people there. We managed to get the labor force survey answered. I don’t find it particularly plausible that that’s hard to do.’

It was typically carried out in person before the pandemic, before collection switched to over the phone during Covid. This in itself was plagued with problems, such as no longer being able to call homes directly since many have abandoned their landlines.

From 2019 to 2023, the response rate fell from 39 per cent to just 13 per cent – potentially affecting the accuracy of the completed study. 

The response rate was above 80 per cent in the early 1990s, per the ONS. 

Adam Corlett, principal economist at the Resolution Foundation, said the government was being ‘left… in the dark’ about the true picture of employment in Britain.

He said last week: ‘The government faces a significant challenge in aiming to raise employment, even if the rate is higher than previously thought.

‘But crafting good policy is made harder still if the UK does not have reliable employment statistics.’

Former ONS statistician Richard Clegg told the Telegraph the survey was being affected by the fact people don’t have time to take part in the study, particularly if they are at work, and were being bogged down by the 200-plus page questionnaire.

‘If dropping below 80pc sounded alarm bells then you can imagine dropping below 20pc really affects quality quite substantially,’ he said.

Workers attached to the PCS union are also preparing to strike on an as-yet-undecided date after being asked to go back to the office two days a week rather than working from home.

Many of these workers are based out of Wales, after the ONS moved its headquarters out of London to Newport in the late 2000s. 

This was done in a bid to boost regional growth but a 2015 review conducted by former Bank of England deputy governor Sir Charlie Bean found that it had a hugely detrimental effect.

Nine in 10 of the staff who had been based in London decided to quit rather than relocate, leading to a brain drain, he concluded.

Further to this, the ONS is facing stiff competition from private firms who can offer more lucrative salaries to the better qualified. LinkedIn job postings show salaries of £35-45,000 for data analysts and statisticians, with 2:2s rather than first-class degrees accepted. 

And the concerns over working from home can themselves be seen in ONS figures, which suggest homebodies work an average of 10 minutes less per week – and sleep for 20 minutes more.

The ONS told MailOnline today that its data on home working is ‘not precise enough to be sure that people spend less time working when working from home’. 

PCS-affiliated workers voted last month to continue industrial action, working to rule by refusing to work in offices or agree to overtime.

General secretary Fran Heathcote claimed the action had ‘no tangible impact on the ONS’ outputs – which was the point, because we said our members can work at home just as well, if not better, than being in the office’.

It can call for a full walkout any time before the beginning of April. 

The ONS says the new methods of recording migration data are an improvement, while it is taking steps to improve the Labour Force Survey’s response rate, such as by cutting the length of the questionnaire and reintroducing face-to-face interviews.

It has previously admitted that data from HMRC and other surveys it was carrying out were ‘likely to be painting a more accurate picture’ than the LFS. 

The ONS told MailOnline today: ‘As far as ONS policy is concerned… we believe firmly that a reasonable level of office attendance – in line with the wider Civil Service – is in the best interests of the ONS and of all our colleagues. 

‘Face-to-face interaction supports personal collaboration, learning and innovation. The current dispute involves only a minority of ONS staff and is having no significant impact on our key statistical outputs.’

Immigration rose sharply after the points-based system for work visas was introduced by Boris Johnson’s government after Brexit to make up for a dearth in EU workers.

Students were allowed to stay in the UK for longer, while the Health and Care Visa for care workers was expanded in December 2021 to encourage a staffing boost in the NHS as well as in adult social care.

Some of these rules were tightened under Rishi Sunak’s government, including on bringing family members and upping salary thresholds, leading to a drop in net migration.