The webcam shows a pile of bamboo shoots in Edinburgh zoo's purpose-built giant panda house. Yang Guang is asleep off-camera and Tian Tian, his possibly pregnant mate, is in a separate enclosure.

Meanwhile, Iain Valentine, the zoo's director of pandas, paces around the Royal Zoological Society of Scotland's office like an expectant father.

If Tian Tian gives birth, it will be in the next few days. If she were to, the zoo's financial security would be assured – even as Scotland decides its political future. A panda cub would be a conservation superstar, attracting millions of visitors at up to £16 a head. But if Tian Tian isn't even pregnant, the zoo faces declining public interest, rising costs and possible financial ruin.

The next few hours are crucial, said Valentine. "We cannot be certain how long it will be before we call it a day with Tian Tian. We are coming to the end. Shortly she will hit what we call base with her progesterone levels and only at that point will we be certain – she will simply either give birth or not."

Parents or not, Tian Tian and Yang Guang are the animal equivalents of Premier League footballers; they cost a fortune to buy and maintain, but are guaranteed to draw crowds. But academic research into "pandanomics" also suggests that they and other captive giant pandas have become strategic assets deployed by China for geopolitical advantage.

According to Valentine, the Edinburgh pair have more than paid their way since they arrived in 2011. "Zoo numbers have increased by four million people in two years," he said.

However, the costs are rising and experience from other zoos suggests that the numbers will tail off if no cub is born. The pandas are rented from the Chinese government for 10 years and the contract stipulates that Edinburgh must pay £600,000 a year for the pair. Any cub that is born must be returned to China after two years. Should one die because of human error, it is understood that the zoo must pay £300,000.

But that is just the start. The zoo had to spend nearly £300,000 to house its pandas and has now been hit by rising bamboo costs. When the pair arrived in 2011, it cost around £70,000 a year to import fresh shoots from France, but this has risen to £100,000, said Valentine. To offset the costs, the zoo has now planted 3,000 clumps.

Having a panda can be ruinous, say some zoos, and could even take money away from other conservation work. Washington, Atlanta, Memphis and San Diego zoos are said to have spent $33m more on pandas from 2000-03 than they received from showing them.

During the cold war, Mao gave pandas away as a sign of diplomatic friendship. But World Resources Institute researcher Kathleen Buckingham, with a team at Oxford University, last year studied China's recent panda loans and concluded that all were linked to trade.

The Edinburgh deal, overseen by China's vice-premier, Li Keqiang, coincided with a £2.6bn contract for Britain to supply China with petrochemical and renewable energy technologies, Jaguar cars and enough salmon to double Scotland's production.

Other panda pairs were loaned to Canadian and Australian zoos after negotiations for uranium, oil and minerals. Singapore, Malaysia, Thailand and Macao all got pandas after signing free-trade agreements In France, the panda loan to Beauval zoo coincided with a $20bn deal for nuclear giant Areva to supply China with uranium oxide.

"A new phase of panda diplomacy is under way. Panda loans are associated with nations supplying China with valuable resources and symbolise China's willingness to build trade relationships," said Buckingham.

She likens the loans to Asian rulers' traditional gifts to foreign powers of rare white elephants in the knowledge that they would cost a fortune to keep but ensure closer relations. "The panda may be the modern-day white elephant – a powerful emblem of the modern Chinese nation," she said.

By next year, 20 zoos outside China are expected to have pandas. The growing numbers sent abroad are thought to be linked to the 2008 magnitude eight Sichuan earthquake, which destroyed much of the animals' habitat. China was left with a surplus of captive pandas, but nowhere for them to go.

Some conservationists argue that with only 1,600 animals left in the wild, foreign zoos are helping to breed a diverse population fit to be released. But critics say only 90 cubs have been born outside China in 35 years.

Links between foreign zoos and Chinese researchers have led to advances in captive breeding, said Valentine. "There are now 340 giant pandas in captivity. China is playing the long game. Until now it has been trying to build up the captive population to between 300 and 500. That's the magic number for genetic integrity. "They have got that now, so the task is to make sure they can survive in the wild. In the next few years we can expect tens of pandas to be introduced into the wild," he said. However, only 10 have been released since 1983, with just two of them still alive.Six were recaptured after suffering significant weight loss, one was probably killed by wild pandas, and another is believed to have died, said Buckingham.

A panda at Yunnan Safari Park, Kunming, is offered moon cakes ahead of the Mid-Autumn festival: few animals released back into the wild have survived. Photograph: Rex

American academic Sarah Bexell, who works at the Chengdu research base in Sichuan, where more than 100 giant pandas have been born, said: "The future is immensely grim for them. "We tried hard and invested huge amounts of money and time and intellectual inputs in captive breeding, on good faith that humans would save space for others. We failed."

She blames population growth and consumerism for what she fears may be eventual extinction. "The Chinese institutions have done a great job, but people don't want to live in poverty and there is no room for people and pandas. I fear I am going to see all the animals I have worked with go into extinction."

Kati Loeffler, a vet and former director of animal health at Chengdu who is now with the International Fund for Animal Welfare in Massachusetts, said China was not interested in conservation. "Conservation there is a joke. It's all about politics and money. If the west was not interested in pandas, the Chinese would start eating them.

"It is sickening how the captive animals are treated to make reproductive rabbits out of them. They are raised in a human-dominated environment. Individuals are not normal pandas, nor will they ever be, and the reserves where they live in the wild are not protected. It's just a big entertainment show."

But back in Edinburgh, Valentine is still hoping that a cub will be born. "I have not given up yet," he said.