One Nation senator Malcolm Roberts received confirmation that his British citizenship had been revoked in December - a full six months after he nominated as a candidate to the Senate.

After a week of pressure over his citizenship status, Senator Roberts finally unveiled a timeline during an interview on Sky News late on Thursday night.

Senator Roberts said he wrote to the British authorities on May 1 last year to ask them whether he was a British citizen, given he was born to a Welsh father in India.

He says he got no response so he wrote again on June 6 - three days before nominations closed - saying that if he was a citizen he fully renounced. He subsequently nominated as a candidate and won a Queensland Senate seat.