A writ has been issued against Chief Constable George Hamilton (pictured), who has responsibility for both the PSNI and its predecessor, the RUC.

A total of 29 people - including a woman pregnant with twins - were killed in the 1998 bombing by the Real IRA.

Solicitor John Fox, representing the families, told The Guardian: “What they want is answers and whether there were failing in the investigation and whether these failings led to the perpetrators escaping justice.”

He said the legal action had parallels with the Hillsborough campaign.

Mr Fox said: “There are similarities because, yet again, the victims are the ones that have to fight for answers while those responsible aren’t held to account. These are innocent victims and they are the ones that have to go through the courts, not the perpetrators.”

The families decided to sue the police following the collapse of the trial of Seamus Daly, a 45-year-old who denied causing the explosion.

The PSNI has 14 days to respond to the writ, after which details of the lawsuit against the force will be lodged in court.

A spokesperson for the PSNI said of the writ: “Once received, we will take time to consider the contents and respond in due course.”

Mr Fox said separate judicial review proceedings are expected to start in the new year over the government’s failure to hold a public inquiry into claims the attack could have been prevented by intelligence agencies.