Apple is developing its own graphics processors to be used in future versions of products including the iPhone, said one of its partners on Monday.

UK-based Imaginations Technologies currently makes the graphics chips used in the iPhone, but said in a statement that Apple will cease to use its tech in between 15 months and two years time because it is making its own. Imagination's shares plunged 69 percent in the wake of the news.

"Apple has asserted that it has been working on a separate, independent graphics design in order to control its products and will be reducing its future reliance on Imagination's technology," said Imagination in a statement.

Apple is currently Imagination Tech's biggest customer and owns an eight percent stake in the business. Imagination makes chips for the iPhone, iPad and Apple Watch and receives a small royalty every time a device is sold.

The company said it had asked for but not received any evidence Apple can make its own chips without violating patents owned by Imagination Technologies. "Imagination believes that it would be extremely challenging to design a brand new GPU architecture from basics without infringing its intellectual property rights," it said.

Apple declined to comment on Imagination Technologies's statement.