British defence experts expressed alarm yesterday after Donald Trump suggested he might undo a multi-billion dollar stealth fighter project that is to form a core part of the United Kingdom's defensive capabilities.

The president-elect took a casual shot at the F-35 programme for the world's most advanced fighter jet tweeting on Monday that the cost was "out of control".

"Billions of dollars can and will be saved on military (and other) purchases after January 20th," he wrote, indicating a change in strategy after his inauguration.