With nearly 11 million cats living in about one in four households, they are Britain’s most popular pet. But until now the size of the country’s stray population has been something of an unknown. In the first study of its kind, researchers have calculated there are nearly a quarter of a million stray cats living in urban areas of the UK – or an average of 9.3 a square kilometre. The research, published in the journal Scientific Reports, found that in some areas the average rises to as high as 57 unowned cats a square kilometre. The lowest is 1.9. The authors said the population may be created from accidental litters and cats being abandoned or straying from home, which then support themselves by scavenging on human food waste. Experts said barriers to neutering, especially during the pandemic, are pushing up stray populations. “Up to now, there haven’t been any evidence-based estimates of the number of stray and feral cats in the UK,” said Dr Jenni McDonald, a feline epidemiologist for Cats Protection and lead author of the research. “It has previously posed a challenge in part because of problems accurately distinguishing owned from unowned cats.” Researchers used data modelled from 3,101 surveys and 877 residents’ reports from five areas – Beeston and Bulwell, both in Nottinghamshire, Bradford in West Yorkshire, Dunstable and Houghton Regis in Bedfordshire, and Everton in Liverpool – over a period of one year. They then paired them with 601 confirmed locations from community teams for the animal charity Cats Protection within a population model to establish key indicators of unowned cat populations. Their findings were then applied to urban populations across the UK in order to form an overall estimate. Of the estimated 247,429 unowned cats, the most concentrated population is believed to be in densely populated and socioeconomically deprived areas. An RSPCA spokesperson said numbers of feral cats were increasing in urban areas of the UK, leading to an “overpopulation crisis”. They said the best way to tackle the problem was to neuter cats from four months old to prevent unwanted litters and to run “trap, neuter and release” programmes for street cats. But they fear the pandemic may have stopped some owners from getting their cats neutered, warning it could lead to “an increase in the number of kittens being born and sadly ending up in rescue centres”. Kelly Grellier, the chief operating officer of pet charity Blue Cross, said people returning to work after lockdown or changed circumstances could lead to a rise in stray cats. “We’d always urge owners who are struggling to care for a pet to get in touch with a charity like Blue Cross for support.”