The families of the victims of Scotland's worst industrial accident in a generation were yesterday assured they would not have to wait too long for answers to what caused the tragedy.

Elish Angiolini, the Lord Advocate, made the pledge as she and Peter Hain, the Secretary of State for Work and Pensions, confirmed a full public inquiry will be held into the explosion at the ICL factory in Glasgow.

Nine people were killed and 33 injured in the blast, which took place on May 11, 2004.

In August, the owners and operators of the factory, ICL Plastics and ICL Tech, were fined £400,000 after pleading guilty to breaches of health and safety procedures over the leaking gas pipe which caused the explosion.

A spokesman for the companies said they hoped the inquiry would "properly establish all the facts and circumstances relating to the disaster".

The full remit and timetable of the public inquiry has still to be finalised, but Ms Angiolini promised that the situation will not be allowed to drag on.

She said: "I am conscious of the anxiety that the families of those who died and the survivors have continued to suffer and both the Secretary of State and I wish to ensure that the inquiry takes place as quickly as possible, and should not be unduly lengthy."

Mr Hain said: "It is essential that the inquiry is thorough, transparent and exhaustive but not protracted. The families have suffered already and we do not want them to have to wait unduly for answers."

The hearing will be the first in mainland Britain under the UK Inquiries Act, which became law two years ago.

It will be held in Scotland under the jurisdiction of both governments as health and safety legislation is reserved to Westminster, while the investigation of deaths north of the border is the responsibility of the Lord Advocate.

Ms Angiolini said she was convinced that was the best way to provide the answers the victims' families have been looking for. She said: "I met members of families, and other interested parties, to consider their views on what it was hoped that the inquiry would achieve.In light of these helpful discussions and the matters uncovered by the investigation team in the course of the preparation for the criminal trial, I concluded the best outcome would be a full public inquiry which comprehensively investigates the events leading up to the tragic explosion, and the issues arising out of that."

Peter Hain said his own meeting with the families had left him "convinced" that a full public inquiry was the best way to proceed. "I welcome the opportunity to ensure that lessons are learned from this tragedy," he said. "The findings are likely to have significance across the United Kingdom."

A spokesman for First Minister Alex Salmond said: "Ministers are very pleased at the announcement of a full public inquiry, which they believe is the best possible option."

Ian Tasker, assistant secretary of the Scottish Trades Union Congress and a spokesman for the victims' families, said: "There are three key questions from the families; why did their loved ones die, why were the failures allowed to build up over an unacceptable period and what changes can be made in legislation to ensure that other families never have to go through what they went through?"

In a joint statement, the local MSP, Patricia Ferguson, and her Westminster colleague Ann McKechin, welcomed yesterday's announcement. "We believe a full inquiry is the only way to do justice by the families and the survivors."