The police officer in charge of solving the case of the “black-cab rapist” John Worboys says similar crimes could still be happening today as the criminal justice system is “close to exploding”.

Tim Grattan-Kane was the senior investigating officer of the team who arrested Worboys in 2008 after they pieced together the accounts of numerous women who had reported being given drugged champagne by a London taxi driver, who then assaulted them.

Grattan-Kane, who is now retired, said the overstretched justice system was “close to exploding with a frightening bang”. He said he knew of young police officers who were frustrated by the system and “waiting to get results from the Crown Prosecution Service, who are underfunded and taking so long to make decisions”. He also said there was a lack of support workers “because of financial cuts” and getting trials for cases was difficult because so many courts had been closed. According to the Law Society, more than half the courts in England and Wales were closed between 2010 and 2019.

Speaking before the broadcast of a new ITV drama, Believe Me, about the women whose testimony convicted Worboys, Grattan-Kane said he believed there remained a “real problem” with “men administering drugs to facilitate sexual assault”.

He pointed to the Gisèle Pelicot case in France, and that of Vikas Nath, a Knightsbridge restaurateur who is facing trial on allegations that he raped and sexually assaulted a woman who had been drugged, which he denies.

Speaking more generally, Grattan-Kane, who has been advising producers at ITV Studios, said drink spiking had become “far more common”, either because more people were becoming aware of it and trying it, or because more men had “a bad approach to women”. He also believed higher rates could be the result of more women reporting their drinks being spiked.

In Believe Me, Grattan-Kane’s team is credited with helping solve the Worboys case after previous Metropolitan police officers made mistakes and missed crucial evidence.

Grattan-Kane and his officers identified links between Worboys’s crimes and went back over previous blood tests and CCTV footage. They also spoke with a person training to become a black-cab driver to predict which routes the attacker might have taken.

Grattan-Kane said officers had “asked victims to come forward [saying] you will be trusted, you will be listened to, you will be believed; which is why the drama is called Believe Me. That is when the phone started to go red hot.”

The Worboys case helped change how the police deal with rapes. Grattan-Kane said the process should start from the point of believing women who claim they have been assaulted. However, the system needed “continued, constant monitoring” to ensure the process was followed appropriately.

He said the police also needed to “think the unthinkable” about people in positions of trust, which was vital in solving the Worboys case. Because he had been a black-cab driver and dropped the women home after he had attacked them, officers did not suspect him. “When the police are investigating these things [they need] to try and keep an open mind. But I’m aware not everyone had the same attitude,” said Grattan-Kane.

He highlighted the murder of Sarah Everard by the off-duty Met police constableWayne Couzens as an example of someone who had used their profession to gain a woman’s trust.

Although the police should not be excused for the mistakes they had made in relation to Worboys, said Grattan-Kane, he acknowledged their response was now “far more centred” on survivors, and that the Met were under pressure at the time after Tony Blair’s government had adopted New York’s target-driven system of holding police officials to account.

Grattan-Kane said if that was how you “measure performance – by numbers rather than quality – you end up with a problem. There’s always a balance to be struck in a process where you want something [that is] victim-focused.”