The environment secretary Andrea Leadsom is under increasing pressure to make good on a Tory manifesto commitment to ban the UK ivory trade after China announced it would close down its domestic ivory market.

Conservation organisations, including a charity championed by Prince William, say that by allowing the trade to continue the UK is fuelling the annual slaughter of thousands of rhinos and elephants. A recent study suggested that the UK is now the third-largest supplier of illegal ivory items to the US.

Boris Johnson, the foreign secretary, a predecessor, William Hague, and a former secretary at the Department for Environment, Food and Rural Affairs, Owen Paterson, all support a total ban, which was a Conservative party manifesto commitment in 2010 and 2015.

But after coming under pressure from the UK’s auction houses and antique dealers, which have mounted a powerful lobbying campaign against such an all-out ban, Leadsom has leaned towards a compromise.

Prince William is patron of Tusk, one of the charities that have linked ivory sales in the UK to the slaughter of 30,000 elephants a year in Africa. Photograph: Adnan Abidi/AFP/Getty Images

Under plans announced last September, Defra intends to ban the sale of items containing ivory produced between 1947 and the present day. However, a trade in works of art and antiques made with ivory and produced before 1947 will be permitted, much to the dismay of wildlife protection charities.

In an open letter to the prime minister, Action for Elephants said that laws to regulate the ivory trade in the UK had proved to be ineffective and unworkable. It warned that the police and the courts did not have the resources to monitor the trade or prosecute cases where the law was broken, and that the new law would only complicate matters. A legal ivory trade, it said, provided cover to criminals to launder illegal ivory through the UK.

But both the British Antique Dealers’ Association (Bada) and the Association of Art and Antiques Dealers (Lapada) vigorously oppose a total ban. Victoria Borwick, Conservative MP for Kensington and president of Bada, used a Commons debate on the ivory trade last month to call on the government to make an exemption for genuine antiques containing ivory, insisting that there was no evidence that they contributed to the sale of poached ivory.

But the announcement by China, the world’s largest market for ivory, that it plans to stop all commercial processing and sale of ivory by the end of March, and shut down its domestic ivory market by the end of the year, has placed the UK’s position under acute scrutiny.

Will Travers, president of the Born Free Foundation, said that elephants across Africa were being killed by poachers in the tens of thousands so that illegal ivory could be laundered by criminal syndicates through legitimate markets. “Strong action by China is crucial to the very future of elephants,” Travers said. “So the announcement it intends to close down its domestic ivory market within a year is therefore very good news.”

Charlie Mayhew, chief executive of the anti-poaching charity Tusk, whose patron is the Duke of Cambridge, described China’s announcement as “hugely encouraging, very welcome”.

“President Xi Jinping should be applauded for recognising the devastating impact that China’s ivory trade has had on Africa’s fast-diminishing elephant population,” Mayhew said. “We very much hope that the closing down of China’s market will bring much-needed respite to Africa’s elephant population and the wildlife rangers who so courageously protect them from poachers.”

Mayhew said the UK had shown leadership on tackling the issue at the Illegal Wildlife Trade conference in London in 2014 but there was now a danger its credibility was slipping away. “The government can no longer delay on its own manifesto pledge. China has stolen a march on the UK and if we are to have any credibility as the host of the 2018 IWT conference, then Andrea Leadsom must enact a total ban here.”

An online petition calling on the government to outlaw a trade responsible for the slaughter of 30,000 African elephants a year is approaching 90,000 signatures, almost the number required for parliament to hold a debate on the issue.