Campaigners have called for the UK to suspend arms sales to Saudi Arabia as it emerged that hundreds of British cluster bombs were exported there in the late 1980s.
Defence Secretary Sir Michael Fallon said 500 cluster munitions were delivered from the UK to Saudi Arabia between 1986 and 1989.
This is the first time the Ministry of Defence has said how many of the devices were exported to Saudi Arabia since it emerged that a "limited number" were used by Saudi-led forces in the war in Yemen.
Liberal Democrat foreign affairs spokesman Tom Brake said: "The fact so many British-made cluster bombs were sold to Saudi Arabia and are now being used in Yemen is a stain on the UK's reputation worldwide.
"Michael Fallon has an urgent responsibility to address this shameful legacy, by suspending arms sales to the Saudi regime and putting pressure on it stop using these horrific weapons.
"Most people are rightly sickened by the bombing of innocent civilians in Yemen, our Government must end its complicity in this conflict immediately."
The UK has faced accusations of war crimes and calls to suspend arms sales to Saudi Arabia over the use of the weapons, which were banned in 2010 in an international treaty signed by Britain.
Last month Sir Michael said he was satisfied that use of the bombs had not breached international law, and he had requested the Saudis destroy their remaining stock of UK-supplied cluster munitions.
But he was unable to tell the Commons how many had been exported in the first place.
In a letter to Tory MP Philip Hollobone, Sir Michael confirmed: "The UK delivered 500 BL755 cluster munitions under a government-to-government agreement signed in 1986.
"The final delivery was made in 1989."
Sir Michael added that the UK has not been able to carry out any surveillance of the weapons since 2008, given that it backed the Oslo Convention which withdrew support for cluster munitions.
Cluster bombs are designed to release dozens of smaller bombs over a wide area, but the smaller munitions do not always explode, posing a major future risk to civilians.
Amnesty International UK director Kate Allen said: "Yemeni children and other civilians are being put at extreme risk of being killed or maimed by unexploded cluster munitions, some of them made in Britain.
"Given that the UK sold these atrocious weapons to Saudi Arabia, you would have thought ministers would be particularly alarmed that the Saudi-led coalition has been spraying them all over Yemeni villages.
"Instead of these limited answers to MPs, we need to see Michael Fallon ordering an immediate suspension all further weapons sales to Saudi Arabia that risk fuelling these appalling atrocities in Yemen."