As Longleat and Whipsnade celebrate significant birthdays Mark MacKenzie assesses their popularity

The huge interest shown in the London whale was a vivid illustration of Britons' love of animals. But while our concern for the plight of those in the wild remains undimmed, attitudes to creatures held in captivity are less well defined.

This year, Whipsnade Wild Animal Park in Bedfordshire celebrates 80 years of opening its gates to tourists. Further west, Wiltshire's Longleat Safari Park celebrates its 40th anniversary as an "animal attraction". According to research by the Born Free Foundation, an animal-welfare charity, the UK is home to more than 250,000 captive animals. Spread among 400 zoological collections, they are part of a global zoo industry running to more than 10,000 venues. With 600 million visits a year between them and an annual operating budget in the region of £2.8bn this is business on a grand scale.

"Our understanding is that the public perception of zoos is becoming more positive," says Ralph Armond, director general of London Zoo. He believes that leading city zoos such as London see themselves as "conservation centres" providing a vital educational resource "driven by the general growth of interest in green issues".

Britain's first zoo was the "Tower menagerie", established by Henry VIII in 1235. London Zoo, arguably the country's most well known, opened to the public in 1847. In the Victorian era the concept flourished, even if the welfare of "exhibits" played second fiddle to an obsession with taxonomy. Longleat, famous for its lions, opened in 1966, and was the first drive-through safari park outside Africa. Today, Britain's zoos and safari parks are regulated under the Zoo Licensing Act, introduced in 1981, and each receives an annual audit to ensure operations meet minimum animal-welfare requirements.

"In the 1950s," says Armond, "zoos attracted large numbers [London Zoo's annual record is two million], but with more competition numbers declined. In the past 10 years we've seen a steady increase; London is now up to 900,000 a year, with Whipsnade approaching 500,000." Armond describes London's as "a 21st-century urban zoo" with a visitor experience to match. In addition to various multimedia displays on site, he emphasises the zoo's contribution to conservation. "The Zoological Society of London [the body that oversees London Zoo and Whipsnade] operates 40 field projects funded by a mixture of gate receipts and sponsorship. In Kenya, we're introducing rhinos in a valley where 30 years ago there were 20,000 and now there are none.

"If we can get across why paying money to see those animals will help save them in the long term, I believe we have an increasing relevance."

It's a view not shared by Will Travers, chief executive of the Born Free Foundation, the organisation made famous by the conservationist Joy Adamson. In 1984, the foundation established Zoo Check, an investigative arm to monitor the welfare of animals in captivity worldwide and which played a key role in drawing up the European Zoos Directive legislation, which requires licensing for all zoos in the EU. Of the global contribution of zoos to conservation, Travers is withering. "It would be optimistic to say that it happens to any great degree. In terms of the bang for buck, payout on the conservation dividend is poor," he says. "For example, two major zoos in Australia [Taronga in Sydney and Melbourne Zoo] are importing elephants from Thailand and spending £25m on two enclosures. In field conservation terms, we could do a hell of a lot with £25m."

He is equally sceptical of the educational experience zoos provide. "People don't learn that much; we would contend they learn more from a well-crafted wildlife documentary."

While he concedes that legislation governing British zoos is relatively progressive, he warns that those planning zoo visits overseas should tread warily.

"In South America, it's hard to find any zoo that would meet the standards required in the UK. And with the exception of those in Johannesburg and Pretoria there are virtually no modern zoos in Africa," he says.

"In countries that are not particularly wealthy animal welfare isn't a priority. That said, we get more reports from Spain than from any other country in Europe. And in North America there are 2,500 display facilities licensed under the US Animal Welfare Act - the minimum legal requirements are pitiful."