Prime minister Tony Blair has pledged this week to overturn a controversial House of Lords decision that deprived thousands of asbestos victims and their families the right to full compensation.

At the GMB conference on Tuesday, Blair backed union calls to reverse a recent Lords' ruling that cut compensation payments to sufferers of asbestos-related cancer.

Blair said: "I regret that judgment. I am looking at the moment to see the best opportunity for us to change it. If we possibly can change it, we will. I hope we will be able to announce something on this within the next couple of weeks."

Trade union UCATT is calling on the government to reverse the decision by amending the Compensation Bill, which is currently going through the House of Commons.

Alan Ritchie, UCATT general secretary, said: "An amendment to the Compensation Bill would be the most expedient way to deal with this gap in justice."

The Lords ruling in Barker vs Corus limits employers' liability where victims worked for more than one company. This has led to concerns about tracing insurers of employers who have ceased trading.

A spokesperson for the Association of British Insurers said it was in talks with the government "to develop the fairest possible system for claimants".

Lawyers have expressed surprise at Blair's proposal to retrospectively change to the law. Patrick Holmes, a partner at law firm Macfarlanes, said: "This would change existing liabilities as stated by the courts. It is not unheard of but it is usually limited to the tax arena."