The Liberal Democrats have renewed their call for the government to publish its legal advice on the war in Iraq.

The party's leader in the Lords challenged the decision by the American administration in Baghdad to open Iraq's economy to foreign investors.

Baroness Shirley Williams argued that the move makes the allied occupation of Iraq illegal.

Williams claimed that under Article 43 of the Hague regulations, changes to administrative structures can only be made for security, public order or humanitarian reasons.

The Liberal Democrats want the government to publish the full legal advice issued by the attorney general ahead of the war in Iraq.

Moves by Iraq administrator Paul Bremer to open up the country's oil and other commercial sectors to foreign investors have been condemned by opponents who question their legality.

"Paul Bremer's decision appears to be illegal and contrary to the Hague regulations, as the attorney general himself confirmed in advice to the prime minister in March," Williams said.

"These so-called 'reforms' are shock-therapy of the sort that did so much damage in post-Soviet Russia.

"They will create resentment among Iraqis and fuel suspicion about the motives of the coalition. This latest decision is further reason for full publication of the attorney general's legal advice."