Swathes of green belt in the heart of England have been earmarked for new homes for people who may never exist, in a trend fuelled by the drive to double the number built annually nationwide, campaigners have warned.

Fields bordering ancient woodlands are among more than a dozen sites, around Coventry, which have been released from anti-sprawl protections. They will be ploughed up to build more than 11,000 new homes based on population growth predictions that demographers warn are likely to be over-inflated.

Want to resolve the UK's housing crisis? Here's how | Larry Elliott Read more

The city council believes it needs land to accommodate 42,400 new homes in the next 12 years, based on population predictions by the government’s Office of National Statistics (ONS), which predict the population will surge by almost a third between the last census, in 2011, and 2031. Green belt in neighbouring areas, including Warwickshire, Nuneaton and Rugby, has also been earmarked for housing to help Coventry meet its target.

Analysis presented at the British Society of Population Studies, in Cardiff, on Tuesday suggested homes earmarked for open fields were being planned for “ghosts”, because there is no wider evidence of the sharp predicted population growth. Just 15,000 new homes were needed, requiring the loss of far less green space.

“If there has been hyper population growth in Coventry, they are ghosts or vampires,” said Merle Gering, a Coventry-based campaigner whose analysis has been endorsed by leading demographers. “They don’t go to school, don’t attend A&E, don’t have babies, don’t own cars, don’t claim state pensions, don’t use gas or electricity, and don’t put waste into their bins … The net result? The death of the green belt.”

Similar fears have been raised elsewhere. Last week campaigners in Birmingham claimed housing need had been deliberately over-estimated after a scheme for 5,000 homes by 2031, on fields near Sutton Coldfield, was halved in size. In January, Andy Burnham, the mayor of Greater Manchester, accused the government of making it impossible to reduce the amount of protected green belt allocated to housing through the use of old population growth figures, which are higher than the most recent projections.

Housebuilders prefer to build on open land because they consider it quicker, cheaper and easier than previously-used brownfield sites. The government wants 300,000 new homes to be built annually by the middle of the next decade – more than double the output over the last 10 years. Campaigners fear planning inspectors are facing political pressure not to query ambitious targets set by councils, even when they involve the destruction of green belt.

“We agree with him entirely in terms of these crazy projection figures,” said John Wareham, the chairman of the Campaign to Protect Rural England in Warwickshire. “Coventry has forecasts of around 30% increase in population compared to Stratford-upon-Avon and others which are 10%, which makes no sense. This land between large urban settlements has been there for many hundreds of years and is valuable for leisure and for farming.”

Housebuilding targets set by councils are based on ONS population projections but Gering believes the figures for Coventry are skewed by a large number of foreign students, many of whom will not settle in the area. The ONS, which said it was always looking to improve its statistics to inform policymakers, said it used methods assessed by experts in the field and “we look to produce these estimates as accurately as we can”.

A spokesperson said: “We will continue to engage with the group of concerned residents in Coventry, as we would with any users who need assistance in understanding our estimates.”

Coventry city council said the population projections and the green belt site allocations were assessed by the government’s planning inspectorate.

A spokesperson said it saw “no evidence at this time that the housing requirements identified within its local plan are wrong or failing”.

It added it “will continue to work with our neighbours to monitor housing delivery and supply to inform any need to review the plan in the future”.

Gering’s analysis of the 2011 census and ONS predictions found the rate of growth predicted for Coventry was well over twice the regional average. He found attendances at A&Es over the last decade grew faster in Wolverhampton, Birmingham and Burton; increases in car registrations grew no quicker than in many other areas; and birth rates fell slightly as in most areas.

There was a lower-than-average increase in gas meters, electricity use fell quicker than in other areas, school admissions were average and the number of people on the electoral roll remained steady from 2011 to 2017. He also checked the volumes of domestic waste and found that it was trending in line with other areas.