The corporation has now appointed an independent barrister to lead a broader review to "fully examine" his conduct during the two decades he spent working there.
It comes as police are believed to be investigating sexual assault allegations against Westwood going back four decades.
The DJ, who has not been named as a suspect by the Metropolitan Police, has previously been accused of a string of sexual assaults against women and has denied any wrongdoing.
In a statement, Scotland Yard said: "Detectives from the Met's Central Specialist Crime continue to investigate four reports relating to allegations of non-recent sexual offences allegedly committed by a man.
"The offences are alleged to have occurred in London in 1982, 1985, 2010 and 2016. There have been no arrests, inquiries continue.
"We would appeal to anyone who has been the victim of sexual crime to contact police. Your complaint will be thoroughly investigated and you will be supported by specialist officers."
The veteran DJ, who left the BBC in 2013, stepped down from his show on Capital Xtra in April following accusations by several women of misconduct and predatory behaviour.
Westwood, 64, "strongly" denies any wrongdoing.
In July, the BBC said it received six complaints against Westwood, including one that was referred to police, despite director-general Tim Davie previously saying he had seen "no evidence of complaints".
Mr Davie subsequently launched an internal audit, reporting to the BBC board's senior independent director, Sir Nicholas Serota.
Following the report's publication on Thursday, the corporation has appointed an independent reviewer to lead a broader review into what was known about concerns raised about Westwood.
Barrister Gemma White, supported by the law firm Linklaters, will aim to complete her investigation in six months and the BBC has said it is willing to work with Westwood's other employers, which include MTV and Capital Xtra-owner Global, to fully establish what happened.
The investigation comes after Lord Dyson's report in May 2021 into how Martin Bashir secured his bombshell Panorama interview with Diana, Princess of Wales.
The new review will not make recommendations about what action should be taken against Westwood or any other individuals "or within the BBC generally".
However, it will look at whether concerns about his behaviour affected the decision not to renew his contract past September 2013.
The corporation also said it is in contact with the Metropolitan Police, and that as part of the "ongoing work any relevant information will be passed to them".
Sir Nicholas said: "I am grateful to the BBC's investigations team for the work they have done.
"It is an important piece of work, but I see it as a first step. New allegations and issues are emerging as time passes and more people are prepared to come forward. For this reason the work must continue.
"In light of the issues identified by the internal review, I have asked, on behalf of the BBC board, that a broader review is now conducted and a full report is produced.
"It is vital that this work is able to command the full confidence of those who have, or may wish, to come forward, as well as the wider public, and it is for that reason the BBC board believes there should be independent oversight.
"I have therefore asked Gemma White QC to lead this work. She is a hugely respected barrister who has relevant expertise and experience in this area.
"I have asked that the next stage of this work be completed within the next six months.
"However, I want to be clear this is not a hard deadline and if new issues emerge, then time will be made available to properly explore them. Our main objective must be to discover the facts."
A statement from a representative of Westwood in April said: "Tim Westwood strongly denies all allegations of inappropriate behaviour.
"In a career that has spanned 40 years, there have never been any complaints made against him officially or unofficially.
"Tim Westwood strongly rejects all allegations of wrongdoing."
His representatives have been contacted for further comment.
The DJ, who is the son of Bill Westwood, the former Anglican bishop of Peterborough - who died in 1999, began his career on local radio before joining Capital Radio in London.
He was later given his own show by BBC Radio 1.
He left Radio 1 and Radio 1Xtra in 2013 after nearly 20 years and returned to Capital Xtra to host a regular show on Saturday nights, where he was referred to as "The Big Dawg".