The father of World's End victim Helen Scott says he will never give up his hopes for justice as a landmark legal move is made to try Angus Sinclair for her murder for a second time.

The Lord Advocate, Frank Mulholland, has applied to the High Court for authority to set aside the 2007 acquittal of Sinclair and prosecute him again for the murders of Helen and her best friend Christine Eadie 35 years ago.

It is the first application of its kind under double jeopardy legislation in Scotland.

The women, who died aged just 17, went missing after they left the World's End pub on Edinburgh's Royal Mile on October 15, 1977. Their naked bodies were found six miles apart in East Lothian the next day.

Both women had been beaten, gagged, raped and strangled.

Sinclair was arrested and charged in 2005 for their murders following a cold case review and advancements in DNA technology. The trial collapsed due to insufficiency of evidence.

The Crown Office was widely condemned at the time for flaws in the prosecution case.

Morain Scott said: "It's the first step on a new venture and we just have to wait and see.

"We are in the hands of the legal profession. I have always had hope for justice and I have never given up on that in all of the 35 years. I will never give that up.

"All I ever wanted was justice, for Helen not for me. It will never leave me. Every time you see something that has happened to a girl on the television, it all comes back to you.

"You think of the parents and you think what they are having to go through. I have had so many ups and downs over the years, but I suppose you learn to put a face on it."

Mr Scott, whose wife died in 1989, said he planned to attend any future trial of Sinclair: "I will be there, but it does depend on the time factors. These things can move quite slowly," he said.

The Double Jeopardy (Scotland) Act 2011 set out five new conditions where an accused could be retried for a crime they were previously acquitted of, including where "compelling new evidence" emerges.

In other circumstances, a second prosecution can also be launched if evidence later emerges that an acquitted person has admitted to committing the offence, or where the original acquittal was "tainted", possibly by witness or juror intimidation.

The prosecution of a person on a more serious charge, if the victim has died after the original trial, is also included in the measures.

The other cases identified by the Crown as having potential to be retried under double jeopardy legislation are the murder of Indian waiter Surjit Chhokar in Overtown Lanarkshire in 1998 with a trial leading to the acquittal of Ronnie Coulter, Andrew Coulter and David Montgomery.

Strathclyde Police officers are currently re-examining evidence linked to the case following a request from the Crown Office.

A new investigation into the murder of drama student Amanda Duffy has also been ordered. She was found in waste ground in Hamilton, South Lanarkshire, in 1992. The 19-year-old had been battered to death, and her nose and jaw smashed.

Francis Auld stood trial for her murder but the jury returned a not proven verdict.

Earlier this year, Nat Fraser was found guilty for a second time of the murder of his wife Arlene, who disappeared in 1989, in a case brought under double jeopardy legislation.

The original conviction was quashed following a ruling from the Supreme Court in London. Fraser is in the process of appealing his second conviction, with a hearing scheduled in Edinburgh next April.

The World's End case is the first one where the Crown Office has sought to quash the original finding of the court.

Sinclair's acquittal was specifically referred to by Justice Secretary Kenny MacAskill when the new double jeopardy law came into force in November last year, after a two-year review by the Scottish Law Commission.