The illegal trade rakes in billions of pounds a year, making it the second most lucrative after drug smuggling, according to the international police body, Interpol.

The BBC's Margaret Gilmore reports from Heathrow

Animals such as parrots, rare tortoises and lizards are stolen to order by poachers from their natural habitat and couriered to the country of request.

Many are illegal because they are endangered species.

Collectors in the UK and places like the US, Japan and the Middle East create the demand for such animals, who are often delivered in cruel conditions and do not survive the trip.

This parrot, now dead...

"There's a very big trade, for instance, in things like parrots. They are particularly beautiful, quite expensive, something that's different and people want to have them," said customs officer Charles McKay.

Crocodiles are the latest desirable item, as of a year ago, with snakes, lizards and even spiders on many collectors' lists, he said.

...was posted alive in this package

Customs officers do spot checks on all consignments of animals through UK ports and airports, as the smugglers' favourite trick is to put illegal animals in with a consignment that has a permit.

When animals are seized they are sent to a holding centre at Heathrow to keep as evidence in future court cases. Most are then found homes in zoos.

Not all animals are smuggled alive - many skins and other parts are seized by customs. And not all live animals survive the journey.

Eleven parrots and cockatoos were captured in Australia, wrapped in packages like drugs and sent alive by post. They all suffocated.

Mike Butcher, of the RSPCA, said tortoises were of particular concern.

"The cruelty involved in smuggling tortoises is immense. They're packed into trays, squashed down on each other. The loss of limb is prolific and there is a high mortality rate," he said.