The ex-Radio 1 DJ, then in his 30s, was described as a “predator" by his accuser in a new BBC documentary.
She came forward after a string of women accused Westwood of abusing his position in the music industry from 1990 to 2020.
BBC News reported some of the women claim to have been under 18 when they encountered Westwood, now 64.
It is illegal in the UK to have sex with a 14-year-old.
Westwood’s agents were approached for comment by the Standard and did not respond.
Claims by the latest woman, named as Esther, feature in a new documentary, Hip Hop’s Open Secret: Tim Westwood, which airs on BBC Three on Wednesday night.
Esther told the BBC she met the DJ at the Arch in Vauxhall in 1990.
She said the star “didn’t look shocked” when she told him her age and said she could keep coming to the club.
Recalling the alleged abuse, Esther said Westwood had asked to meet her at Hammersmith Station where he picked up her in his car.
It is claimed Westwood drove her back to a flat and offered her a drink, which Esther refused, before he kissed her.
She alleged: “I was like, OK, I don’t have a problem with that. And then, it progressed from there. We had sex.”
Esther alleged Westwood continued to call her after the night and she “never” gave her consent.
She claimed she broke off contact with Westwood when she turned 16 and described herself as “prey”.
In April, a number of women accused the rap DJ of predatory and unwanted sexual behaviour and touching in incidents between 1992 and 2017.
BBC News and the Guardian investigated the claims of 10 accusers who came forward after the initial revelations.
Another claimed she was 16 when the DJ, who was in his 40s at the time, began what she says was a “controlling” relationship with her.
Two other women claim they were in their mid-teens when they were sexually assaulted by Westwood.
Westwood previously strenuously denied the allegations of seven women who featured in the original investigation.
A spokesman said at the time: “Our client confirms that there has never been any complaint made against him, whether officially or unofficially, relating to claims of inappropriate behaviour of the nature described.”
None of the 10 women, all black, reported the incidents to police and all but one have asked to remain anonymous.
The BBC, where Westwood worked as a presenter for 20 years, subsequently revealed it had received six complaints against him, including one referred to police.
Its director-general Tim Davie said earlier this week the corporation is undertaking a “full deep dive” and plans to deliver a report on the complaints within the next two weeks.
The internal audit will report to the BBC board’s senior independent director Sir Nicholas Serota.
Westwood has stepped down from his weekly Saturday night radio show on Capital Xtra “until further notice”.
He is the son of former Anglican Bishop of Peterborough Bill Westwood.
Westwood rose to fame hosting the first nationally-broadcast rap show on UK radio from 1994 and won a number of MOBO awards.
In 1999, he was seriously hurt in a drive-by shooting.