A UK minister has resigned saying that the Kingdom's withdrawal from the European Union's (EU) Galileo satellite-navigation system exposes Theresa May's Brexit deal as "naive".

British science and universities minister, Sam Gyimah, quit Prime Minister Theresa May's government on Friday, the sixth minister to resign in protest of her proposed Brexit deal with the EU.

Earlier on Friday, May conceded that Britain will not use the EU's Galileo space project for defense or critical national infrastructure, following a row over the post-Brexit future of the planned rival to the U.S. Global Positioning System.

It's reported that the UK had wanted to remain part of the project after Brexit, but the EU said it would be banned from the extra-secure elements.

To find a replacement, the UK Space Agency is reportedly looking into creating a British system that can be used to guide military drones, run energy networks and be used on people's smartphones. 

In Gyimah's eyes, the UK's withdrawal means that any deal with Brussels would be "EU first". 

The UK's interests "will be repeatedly and permanently hammered by the EU27 for many years to come," said Gyimah in his Facebook. 

Gyimah, a junior-ranking minister who campaigned in the 2016 vote to keep Britain in the EU, said that the prime minister should not rule out the prospect of a second referendum.

His resignation represents a further blow to May, who is trying to persuade her own lawmakers to approve the deal she struck with Brussels on Sunday.

May faces criticism from all sides including the Northern Irish party propping up her government, ahead of Britain's departure from the EU in four months.

"It has become increasingly clear to me that the proposed deal is not in the British national interest, and that to vote for this deal is to set ourselves up for failure," Gyimah wrote in a resignation statement published by the Daily Telegraph newspaper. "We will be losing, not taking control of our national destiny."