A fresh inquest is to be held into the death of Susan Nicholson, who was murdered by her boyfriend Robert Trigg, after her parents won a High Court challenge.

Ms Nicholson, 52, was murdered in 2011, five years after Trigg killed another lover, 35-year-old Caroline Devlin, in 2006.

Neither death was initially deemed suspicious by police. Ms Nicholson’s parents, Elizabeth and Peter Skelton, brought a legal challenge against the senior coroner for West Sussex over the scope of a fresh inquest into their daughter’s death.

Lawyers for the couple claimed the senior coroner was wrong not to order a full inquest into the death, arguing there were police failings in the case which should be examined.

In a ruling yesterday, Lord Justice Popplewell and Mr Justice Jay allowed Mr and Mrs Skelton’s challenge, ruling a full inquest must take place. In their judgment, the senior judges said they were not finding that the police “were in fact guilty of any failings, or in breach of the operational duties”.

They said: “Our conclusion is merely that that can credibly be suggested, so that an inquest should look into whether that is so.

“It may find no criticism of the police is justified, or that any criticisms are isolated failures and not serious. That will be a matter for investigation at the inquest.”

Mr Skelton said the family is “relieved” at the ruling and hope they will now be able to get the answers they need at a fresh inquest.

He said: “We are really relieved now and feel we are getting somewhere because there will be another inquest and we hope we will get the answers we have been waiting for.

“We might have to wait a few months for the inquest but we are certainly making progress.”

Trigg was jailed for at least 25 years in 2017 for Ms Devlin’s manslaughter and Ms Nicholson’s murder.

After his conviction, the High Court quashed the original inquest into Ms Nicholson’s death, which made a finding of accidental death, and ordered a new inquest be held.

The senior coroner for West Sussex ruled this would be a fresh short inquest, with no witnesses questioned.

Heather Williams, QC, barrister for Mr and Mrs Skelton, told the High Court at a hearing earlier that the couple had argued to the coroner the “circumstances leading up to Susan’s death involved arguable breaches by Sussex Police”.

They said there should be a full inquest under Article 2, the right to life, of the Human Rights Act, which can scrutinise the role of public bodies in a person’s death.

Ms Williams said the couple had argued the force had breached its duty to “take reasonable steps to protect against the real and immediate risk to life posed by Robert Trigg towards Susan Nicholson” as well as its duty to “conduct an effective investigation into a death that may amount to the unlawful taking of life, in relation to Caroline Devlin”.

In her ruling last year, the senior coroner “indicated she was not satisfied there was an arguable breach of either of these obligations and that accordingly she was not obliged to conduct an Article 2 compliant inquest”, Ms Williams said.

It is this decision Ms Nicholson’s parents challenged at the High Court. The senior coroner remained neutral in the challenge.

Sussex Police, which is an interested party in the case, argued Mr and Mrs Skelton’s claim should be dismissed.

Lawyers for the force argued the senior coroner’s decision was not unreasonable.

Mr Skelton accused the force of making the process “much harder and more stressful” by arguing against the request while “threatening us with a large bill of costs if we had not been successful”.

He added: “We want to know whether Susan’s death could have been prevented, so this doesn’t happen again and other families don’t have to go through the pain and distress that we have.”