A study shows that growing numbers of domestic cats are being infected with the deadly form of the disease that is normally found in cattle and badgers.
It is feared one in a thousand could be carrying the mycobacteria, a much higher number than first thought.
Cats, who love roaming, can pick up the disease while exploring countryside badger setts or coming into contact with infected rodents and cattle or contaminated milk.
The risk of passing it on to humans is worrying because Britons are no longer routinely inoculated against TB. The nationwide school vaccination programme was scrapped controversially in 2005.
Professor Danielle Gunn-Moore, who led the research team from Edinburgh University, said: “The potential incidence of feline mycobacteriosis is higher than previously thought. My biggest concern is this is spilling over from cattle and badgers into cats, and poses a risk to cats.
“We are seeing about one per cent of samples sent to labs infected with mycobacterium, which is scary.
“That is why we are keen to raise awareness so vets can look out for it.”
Carl Padgett, a former president of the British Veterinary Association, said: “Cats with TB tend to have close contact with humans. That is where you ramp up a degree of public health risk through direct contact with cats that have TB.”
Between 1994 and 2011, there were 570 cases of bovine TB in humans – although the majority of cases were in people who had drunk infected milk.
The number of people diagnosed with TB in the UK is also rising with nearly 9,000 cases reported in 2011.
Prof Gunn-Moore claimed the risk of humans catching bovine TB from their pets was still “tiny”.
She added: “I have not seen any cases of humans being infected by cats.”
But chief veterinary officer Nigel Gibbens confirmed that cats did present a growing threat to humans.
He said: “Transmission to people is possible and has happened although the number of cases in pets is low.
“Cats seem to be more frequently infected and that could be because of the way they behave.
“They roam and explore and could get into fights with infected feral cats and badgers themselves.”
Researchers at the University of Edinburgh Royal School of Veterinary Studies found that in one year 17 per cent of the 187 cats diagnosed with TB had the bovine strain.
Their study was published in the latest edition of the journal Transboundary and Emerging Diseases.