The Department for Environment, Food and Rural Affairs (Defra), the government department responsible for the legislation, said primates needed zoo-level welfare standards and it was working with local authorities on how to enforce the scheme.
But only a small number of licences have been granted, with none issued in Kent, the BBC has found.
Animal welfare experts warn thousands of monkeys could be put down in a potential “mass euthanasia” of primates as a result.
Bearman’s garden, in Rochester, is never quiet. The marmosets share the garden with the other family pets: a rabbit, two tortoises and a dog.
The marmosets are among the 3,000 to 5,000 primates the government estimates are kept privately across the UK.