The Duke of Cambridge has issued a stark warning about the future of the rhino and elephant as he celebrated a leading conservation charity working to protect Africa's wildlife.

William said the endangered species were threatened with extinction within a few decades and that illegally hunting the animals for their horns or tusks was "barbaric".

His comments came as he gave the keynote speech at a fundraising ball marking the 25th anniversary of the organisation Tusk Trust which William has supported for almost a decade as royal patron.

The black-tie dinner was held in the sumptuous surroundings of Syon House, the home of the Duke of Northumberland, and among the 500 guests were Dragons Den stars Deborah Meaden, a Tusk Trust patron, and her guest Peter Jones and ex-dragon Theo Paphitis.

William greeted the Dragons then made them laugh when he said: "I've watched Dragons Den many times and seen you and your grilling sessions."

Singer Joss Stone entertained the guests and money was raised by an auction of luxury items and opportunities.

In the main speech William said: "The need to protect wildlife in Africa is greater than ever before. You'd have thought we learnt the lessons years ago in the great campaigns to 'Save the Whale' or 'Save the Polar Bear'. But sadly we haven't.

"The elephant and the rhino, among others, are going the same way and, unbelievably, will be extinct in the wild within a few decades, or even less."

He added: "The illegal slaughter of elephants and rhino for their horns is barbaric, and it's not stylish to be associated with it."

William has supported Tusk's work privately and publicly on many occasions.

He visited Tusk projects in Botswana in 2010 with brother Prince Harry and launched the Tusk Conservation Awards three years later.

The Duke recently announced Edward Ndiritu from Kenya as the winner of the first Wildlife Ranger Award on World Ranger Day. This new Award, instigated by William, has been created to recognise the perilous work of those on the frontline of conservation.

Founded in 1990 by Charlie Mayhew, the charity aims to secure a peaceful co-existence between Africa's wildlife and its people and was the second patronage taken up by the Duke after his involvement with the homeless charity Centrepoint.

Mr Mayhew told the guests: "Whilst we are thrilled to celebrate this significant milestone for the charity, the current poaching crisis is a stark reminder that our work is not done. The next 25 years will be a defining period for the survival of many keynote species in Africa."