A lawmaker in British Prime Minister Boris Johnson's Conservative Party has been charged with sexual assault, prosecutors said on Friday, an allegation he denied.

Imran Ahmad Khan, who represents the Wakefield constituency in northern England, is accused of one offence of sexual assault, relating to an incident in 2008, the Crown Prosecution Service (CPS) said in a statement.

"The CPS made the decision that Khan should be charged after reviewing a file of evidence from Staffordshire Police," Rosemary Ainslie, head of Special Crime, said. "The CPS reminds all concerned that criminal proceedings against Khan are active and that he has a right to a fair trial."

Khan, who captured his parliamentary seat from the opposition Labour Party in the 2019 election, said the allegation from 13 years ago was "denied in the strongest terms".

"This matter is deeply distressing to me and I, of course, take it extremely seriously," he said in a statement. "To be accused of doing something I did not do is shocking, destabilising and traumatic. I am innocent."