London: Britain's former defence secretary has urged Theresa May to delay a final decision on whether Huawei should be allowed to build the 5G network until after a new prime minister and national security team is in place.

Speaking to The Sydney Morning Herald and The Age in London, Sir Michael Fallon- who served as defence secretary under Mrs May and her predecessor David Cameron - said the call was too important to be made in the dying days of the Prime Minister's tenure.

"This isn't the kind of decision that can be left to an outgoing prime minister's wash-up," Sir Michael said.

Former defence secretary Michael Fallon wants the United Kingdom to delay a decision on the 5G mobile network. Credit:AP

Pushing back the final verdict opens the prospect of the United Kingdom reversing course and following Australia's lead in banning the Chinese telecommunications giant from the critical 5G mobile network.