Licences to export substances which could be used in the production of chemical weapons to countries including North Korea, Libya and Burma have been granted by the British government in the last decade, MPs were told.
The Committees on Arms Export Controls challenged Foreign Secretary William Hague about the "very disturbing" exports of "dual-use" chemicals, which have legitimate commercial uses as well as the potential for use in weapons programmes.
Mr Hague said that any export licences would have been checked against strict criteria and officials said the decisions would have included an assessment of the risk of the substances being diverted to military use.
Concern over dual-use chemicals has increased since it emerged that export licences for Syria were granted for substances used in toothpaste manufacture but which could also be used for the production of Sarin nerve gas.
Following the revelations about Syria, Business Secretary Vince Cable was asked to supply the committee with a list of licences approved since 2003 for the export of dual-use substances to other countries which either had stockpiles of chemical weapons or were not signed up to the convention banning their use.
Committee chairman Sir John Stanley told Mr Hague: " They include Burma, North Korea, Egypt, Iraq, Israel, Libya, Russia and the USA.
"Have you and the Business Secretary combed through this list and other applications to such countries that are in front of you and a re you making any changes of policy in the light of those revelations, which many of us will find very disturbing?"
Mr Hague told him: "In some of those countries the policy will have changed in any case since 2003. They could be licences issued before such a policy change.
"In other cases it's possible such licences are for the sorts of things we have just been talking about on Syria - while they may be dual use they may credibly be for the manufacture of toothpaste, so it's very important to bear those things in mind.
"They will all have been tested against the consolidated criteria and I would be very concerned to hear if any of them hadn't been."
Richard Tauwhare, head of the Foreign Office's arms export policy department, told the committee: "Anything that is controlled is checked against the consolidated criteria and if it is not in breach or crossing the threshold of the criteria we would have to consider whether, for example, it is covered by an embargo.
"If not then there is no reason to refuse a licence. I admit that some of those countries are non-members or non-signatories to the chemical weapons convention, as indeed was the case with Syria, but that in itself is not sufficient reason to refuse a licence."
Tory MP Sir John asked: "Why should we have been exporting sodium sulphide, which is a dual-use chemical, to a country like North Korea?"
Mr Tauwhare told him: "These things have legitimate commercial uses, they are dual-use chemicals and I don't know this specific example, but I have to assume that it was the case that there was a legitimate and credible commercial end use, it was checked against the risk of diversion to a chemical weapons programme and considered in that case that there was not sufficient grounds to refuse it."
Mr Hague also insisted there was no complacency about the arms export licence system, despite the approval of more than £12 billion of exports to regimes with poor human rights records.
"We are never complacent about these things," he said. "I have seen over the last few years how rapidly issues can arise on export licences."
Around 300 licences a year were now referred for ministerial approval, compared with 39 in 2010, Mr Hague said.
Sir John asked if it came as a surprise that arms export licences to the 27 countries of most concern over their human rights records were worth more than £12 billion.
Mr Hague told him: "Not really, this is a large industry for this country. There is a legitimate trade, we don't have a trade ban with those countries of concern."
He added that one of the countries on the list was China, the world's second largest economy.