In a hawkish speech in London, Defence Secretary Gavin Williamson said leaving the European Union was an opportunity for Britain "when we must strengthen our global presence".

Williamson announced plans to invest pound7 million (8 million euros, $9 million) in the drones, saying he expected squadrons "capable of confusing and overwhelming enemy air defences" to be ready by the end of 2019.

Williamson also said Britain would spend pound65 million in "offensive cyber", and bring two new naval vessels into service for operations from crisis support to conflict.

Opposition parties criticised Williamson's rhetoric.

"The idea that our membership of the European Union restricts us is the purest nonsense," Labour MP Chris Leslie said.

"In fact the economic damage that Brexit threatens is what will most quickly weaken our forces," the anti-Brexit MP said.

Britain is weeks away from its scheduled departure from the European Union and still has no firm arrangements in place.

Prime Minister Theresa May's Downing Street office played down another of Williamson's suggestions, to deploy Britain's new aircraft carrier, HMS Queen Elizabeth, in a challenge to China in the Pacific.

"The full details of her deployment will be agreed by the prime minister in due course," May's spokesman said.

The spokesman said the ship would only be ready to sail in 2021 and its first operational mission would include the Mediterranean, Middle East and Pacific regions.