A full public inquiry into the Stockline factory blast in Glasgow which killed nine people and injured 33 others is expected to be announced on Monday.

The decision was made yesterday after discussions in London between Elish Angiolini, the Lord Advocate, and Peter Hain, Secretary of State for Works and Pensions.

Mr Hain, who met seven of the victims' families on a visit to Scotland earlier this month, is understood to have returned to London determined that the demands of the families for a public inquiry be met as soon as possible.

The owners and operators of the Maryhill factory, ICL Plastics and ICL Tech, were last month fined £400,000 for breaches of health and safety procedures which led to the explosion in May 2004 - a sentence branded by families as an insult. It was Scotland's worst industrial accident in almost 40 years.

It is understood Mr Hain, whose department has responsibility for health and safety, would have preferred a fatal accident inquiry because it could have come to a brisk conclusion, allowing lessons to be learned more quickly but concerns over the efficacy of the FAI system ruled that out.

Ian Tasker, assistant secretary of the Scottish TUC, who is a spokesman for the victims' families support group, last night said the families had not yet been informed of any decision.

He added: "A public inquiry is preferred to an FAI because it could make stronger recommendations that could lead to legislative changes in reserved areas, such as health and safety."

An aide to First Minister Alex Salmond said: "We welcome any inquiry that can look into the full lessons of the Maryhill disaster."