A driver who ploughed his car into a knife attacker in a desperate attempt to stop him killing a mother-of-two has been released without charge.

The Metropolitan Police said that investigators had reviewed the law around self-defence and defence of another, and now considered the 26-year-old “a vital witness” rather than a suspect.

Yasmin Chkaifi died in Maida Vale, west London on January 24 when she ambushed in the street by her ex-husband Leon McCaskie, who also used the surname McCaskre, and stabbed several times.

A number of witnesses tried unsuccessfully to stop McCaskie, before the driver ran him over in a blue Renault. McCaskie was pronounced dead at the scene.

Detective Chief Inspector Neil Rawlinson said: “Having reviewed the CCTV evidence and taken statements of numerous members of the public and attending officers, as well as reviewing the legal position regarding self-defence and defence of another, a decision has been taken that the driver of the car, a 26-year-old man, will face no further police action.

“He is considered a vital witness to our investigation and will be offered support from professionals to help him come to terms with the terrifying situation he was confronted with.

“It is vitally important that when a person dies there is a thorough investigation into all of the circumstances and this has taken place. Such decisions must be thoroughly examined and while this process takes time this has been a priority for my team. The man’s legal advisers have been informed of this decision.

“Inquests have opened in relation to both deaths and my team will continue to work to provide evidence for the coroner. We continue to appeal for witnesses to this incident who have yet to speak to police to come forward and do so.”

Thousands of people signed a petition in support of the driver, and members of Ms Chfaiki’s family were also reported to have hailed him as “a hero”.

He was initially arrested on suspicion of murder, and on Tuesday his lawyer Mohammed Akunjee posted a statement on Twitter expressing the driver’s gratitude for the outpouring of support.

He said: “I am grateful that they have taken this sensible course of action. I will of course continue to assist them and any Coroner’s inquest should the need arise.

“I once again wish to express my gratitude to the British public who supported me so vocally at this most stressful and trying time. I also wish to express my gratitude to my solicitor Mr Akunjee who supported myself and my family through this process.

“I hope that in my actions a message has been sent to society: should you see an evil it is a duty upon you to stop it with your hands, if you cannot then you should stop it by speaking out, if you cannot then at the very least you should hate it with your heart.

“May peace be upon you all.”