Stockpiles of chemical weapons have been discovered in Libya, David Cameron has said, suggesting Colonel Gaddafi lied to Western governments when he promised to get rid of his weapons of mass destruction.

Gaddafi's pledge to surrender any chemical weapons in his possession was key to efforts in 2004 to normalise relations between Libya and the West.

Tony Blair played a key role in bringing Gaddafi in from the cold. But if the reports are true it suggests the-then prime minister was duped by the dictator.

Last night Cameron said Libya's new government had discovered previously unknown stocks of weapons.

"Although Gaddafi agreed to declare and dismantle all his weapons of mass destruction, in the last few days, we have learned that the new Libyan authorities have found chemical weapons that were kept hidden from the world," he said.

When Libya joined the chemical weapons convention in 2004 it had to declare all of its chemical weapons and agree to destroy them.

Gaddafi's regime declared possession of 25 metric tonnes of bulk mustard agent and 1,400 metric tonnes of precursor chemicals, which are used to make chemical weapons.

The scale to which Blair was deceived by Gaddafi is unknown and the Guardian reported that the Foreign Office has dispatched a team of inspectors to Libya to investigate the new find.

Former US secretary of state Condoleezza Rice recently cited the believed disarming of Gaddafi as one of the Bush administration's foreign policy successes.

She told USA Today she was "grateful we disarmed [Gaddafi] of his most dangerous weapons. Sitting in that bunker, I'm pretty sure he would have used them."

And Tony Blair defended his approach to the old Libyan regime in an apperance on the BBC's Andrew Marr show on Sunday,

"He was developing a nuclear and chemical programme," he said. "He gave it all up."

"And in a way, particularly after 9/11, you wanted to say look if you do that, we're going to welcome you back into the international community, and you know he was on state visits to France and Italy and so on as well as us changing our relationship with him."