Victim support groups are calling on MPs to back a new law allowing police to take proactive measures to establish whether a serious offender has a new partner, and if so to inform them of his previous convictions. The call comes after the jailing of serial killer Theodore Johnson, 64, who strangled and battered his ex-girlfriend, Angela Best, 51. He was sentenced to life with a minimum of 26 years on Friday.

Johnson was first convicted of manslaughter in 1981 after throwing his then wife, Yvonne Johnson, off a ninth-floor balcony in Wolverhampton. In 1992 he strangled a second partner, Yvonne Bennett, and pleaded guilty to manslaughter on the grounds of diminished responsibility because of depression and a personality disorder. He was detained in a psychiatric hospital for just two years before being released back into the community.

He kept his past secret from his partner and was let out by a mental health tribunal in 1997 on condition that he agree to supervision in the community and to alert doctors and social workers if he formed any new relationships, something he repeatedly failed to do.

Johnson’s lawyer, Annette Henry, said the mental health tribunal’s condition on Johnson’s release was flawed as it relied on “self-reporting” any new relationship. “This was a dilemma and the tribunal found it was fraught with difficulty in trying to monitor,” she said.

Johnson is not an isolated case. Liliya Breha, the mother of a five-year-old boy beaten to death by her boyfriend, Marvyn Iheanacho, was never warned by probation officials that he had a history of domestic violence and had once tried to strangle a child.

Harry Fletcher, of the Victims Rights Campaign, which is leading calls for change to the laws on domestic violence disclosure, said he knew of many cases where women were unaware of the violent histories of their partners.

Theodore Johnson had previously been convicted of throwing his wife her off a balcony and strangling another former partner. Photograph: Metropolitan Police/PA

In 2016, according to the latest figures available, 113 women were killed by men in England, Wales and Northern Ireland – and 90% knew their killer, according to the latest Femicide Census. The British Crime Survey estimates 1.3 million women suffered domestic abuse in the year to March 2016. Over the same period there were just over 100,000 domestic abuse prosecutions.

Under “Clare’s law”, the domestic violence disclosure scheme introduced in 2014, police can inform a woman of a new partner’s past, but this depends on a woman making an inquiry.

“In a number of recent disturbing cases, women entering into new relationships have found out in tragic circumstances that their new partner has previous convictions for violence, even murder,” Fletcher said. “Victims can refer to Clare’s law and ask the police in specific circumstances if the potential partner has any relevant criminal convictions. However, not surprisingly, that power is rarely used.”

Under the new law that Plaid Cymru MP Liz Saville Roberts hopes to introduce via an amendment to the government’s domestic violence bill, police would be duty bound to create a database holding the convictions and cautions of anyone found guilty of offences including manslaughter, murder, rape or repeated instances of domestic violence or coercive control. Officers could make unannounced visits to offenders, who would face prison if they failed to inform the authorities they were in a new relationship. Police would then have the right to inform the woman of a new partner’s convictions.