A “Hillsborough law” will be introduced in Parliament before the next anniversary of the 1989 football stadium tragedy, Sir Keir Starmer will promise.

The prime minister is expected to announce that legislation that would force public bodies to co-operate with investigations into major disasters will be in progress before April 2025.

A terrace crush at an FA Cup semi-final in Sheffield on 15 April 1989 resulted in the deaths of 97 Liverpool fans.

The prime minister will also announce that work has already begun to recruit a new independent public advocate (IPA) to represent disaster victims and their families.

The Hillsborough Law will introduce a legal duty of candour on public bodies.

Officials or organisations that mislead or obstruct investigations could potentially face criminal sanctions.

Sir Keir will say he is honouring a commitment he made during a speech in Liverpool two years ago.

He is expected to say: “That was when I promised, on this stage, that if I ever had the privilege to serve our country as prime minister, one of my first acts would be to bring in a Hillsborough Law – a duty of candour.

“A law for Liverpool. A law for the 97. A law that people should never have needed to fight so hard to get. But that will be delivered by this Labour government.”

Margaret Aspinall, who lost her son James at Hillsborough when he aged 18, said the fact Sir Keir had phoned her last night to explain what the new legislation would look like, was “respect for all the hard work” the families and survivors.

“This is about the ordinary people who’ve stayed together,” she said.

“Who stayed together and fought for so long to achieve this. Its took a long time but we’ve achieved it.

“It is a lovely legacy of the 97. Their deaths will have changed things so much for the good of the ordinary people.”

Charlotte Hennessy, whose father Jimmy died in the disaster, has since campaiged for the truth about what happened.

She said it was only after the Hillsborough Independent Panel report she “realised the extent of how much information was withheld from us as a family”.

“Hopefully going forward this will stop other people from having such a long fight to find out what happened to their loved ones,” she said.

It is expected the duty of candour will be supported by a code of ethics for public bodies and authorities.

This is intended to address a “culture of defensiveness” seen in the wake of disasters such as Hillsborough and the Grenfell Tower fire, as well as scandals involving infected blood, Windrush, and the Post Office Horizon IT system.

Mayor of Greater Manchester Andy Burnham, who was responsible for setting up the Hillsborough inquiry when he was Secretary of State for Culture, Media and Sport, said: “It says something about the measure of [Keir Starmer] that he is coming straight back to deliver on the commitment to the Hillsborough families and others.”

He said the law was not about solely about “the injustice of Hillsborough, it’s about future cover-ups… and active cover-ups”.

Burnham added that he believed the changes the law would bring could make a huge difference to the veterans affected by being forced to witness nuclear bomb testing in the 1950s whom he said he firmly believed were victims of a Ministry of Defence cover-up.

The draft new law will see the government take forward recommendations made by Bishop James Jones in his 2017 report which examined the experiences of the Hillsborough families in the years following the disaster.

An IPA would be sent to the scene of any future public disaster, playing a pivotal role in ensuring victims, survivors, and bereaved families get the information and support they need.

The advocate is expected to be in post by next summer. They would inform victims about sources of support, legal advice and services available to them.

The role would also help victims understand actions taken by public authorities in relation to the incident, including how to navigate inquiries, inquests and other formal processes that may follow a public disaster.

The IPA would also communicate with public authorities on behalf of victims.