More than £5m has been recovered in taxes by a taskforce tackling dishonest breeders selling puppies on the black market.
The team was established in 2015 after discussions with animal welfare groups suggested tens of thousands of puppies were being sold illicitly every year, often being kept in horrible conditions.
Officers uncovered fraudsters selling puppies for a huge profit and failing to declare their sales.
Using a range of civil and criminal enforcement powers, HMRC has recovered £5,393,035 in lost taxes from 257 separate cases since the formation of the taskforce.
Mel Stride, financial secretary to the Treasury, said: "It is utterly appalling that anyone would want to treat puppies in such an inhumane way and on such a scale.
"It's also deeply unfair to all of the legitimate businesses who do pay the right tax and the total recovered by the taskforce is equivalent to the annual salaries for more than 200 newly-qualified teachers.
"We continue to work hard with other government agencies and our partners to tackle these traders. We urge anyone with information about tax evasion to report it to HMRC online or call our fraud hotline on 0800 788 887."
HMRC is also involved in Operation Delphin - a multi-agency collaboration across the UK and Ireland designed to tackle illegal puppy smuggling.