The new Hillsborough law will be introduced before the next anniversary of the disaster, Keir Starmer will promise at the Labour party conference in Liverpool.

The new legislation will introduce a legal duty of candour to all public bodies, with potential for criminal sanctions for any official or authority that misleads or obstructs investigations. The current legal duty of candour requires care providers to be “open and transparent with people who use services”. This includes providing support, truthful information and an apology when things go wrong.

Campaigners, who include family members of the 97 Liverpool fans who were crushed to death at Hillsborough stadium in 1989, have been calling for such legislation for years as part of their 32-year fight for justice.

Starmer will promise to introduce the Hillsborough law in parliament before the next anniversary of the tragedy in April. He will say he is acting on a promise he made two years ago to change the law if he became prime minister.

“For many people in this city, the speech they may remember was the one here, two years ago. Because 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.”

The prime minister will add: “Today I can confirm that the duty of candour will apply to public authorities and public servants, that bill will include criminal sanctions, and that the Hillsborough law will be introduced to parliament before the next anniversary in April.”