The Business Department approved a licence to export potassium flouride and sodium flouride last January, months after violence broke out in the war-torn country.
The government said no chemicals were exported before the licence was revoked in June 2012 following EU sanctions but members of Parliament have said that the foreign secretary and business secretary could be 'pressed' on the issue.
Labour MP Richard Burden told the Huffington Post UK: “I think many people reading the news that the UK government approved licences for these chemicals will be highly concerned. In 2012 the country was facing severe internal repression and was the focus of international humanitarian concern.
Burden, member of the Commons Arms Export Committee, added: "It’s unfortunately yet another example of the major contradiction between our arms exports and human rights policy. l am sure this is an issue which the Committee on Arms Exports Controls will want some clear answers from Ministers”
“This is an issue I hope the Committee will look at in detail in our 2013-2014 inquiry, in which we will be specifically looking at the arms export licences granted to the 27 FCO countries of human rights concern. The secretaries of state for BIS and FCO both give evidence to the committee, and we will certainly be pressing them on this case.”
“In theory, the UK’s arms export controls are rigorous, but our Committee’s investigations show that the practice does not live up to the theory.”
The Commons Committees on Arms Exports Controls (CAEC) said supplies of sodium fluoride, which could be used to produce chemical weapons, had been exported to Syria in the last few years.
"The scale of the extant strategic licences to...countries of human rights concern puts into stark relief the inherent conflict between the Government's arms exports and human rights policies," said CAEC chairman Sir John Stanley.
Deputy prime minister Nick Clegg defended the decision to grant chemical export licences to Syria, saying: "I think it's very important that everyone understands that these licenses were revoked, so these substances were not exported by British companies to Syria."
Syria received nearly £624,000 in British exports of "machinery and transport equipment” during the same period and just over £200,000 in parts for "nuclear reactors and boilers" over May and June 2013.
Amnesty International UK's arms control expert Oliver Sprague told the Huffington Post UK: “Where licences have been issued because the products are sensitive, it’s important that extra safeguards are put in place to ensure that materials are not at risk of being converted for military use or other unintended uses. We’d like to know if that has been done.
The United States says it believes chemical weapons were used by Syrian president Bashar Assad's regime on the outskirts of Damascus on 21 August. It put the death toll at 1,429, including 426 children.
The SNP's Angus Robertson said: "This is utter hypocrisy from the UK government - deploring chemical weapons in public whilst approving the sale of items needed to make them.
"I will be raising this at Westminster as soon as possible to find out what examination the UK government made of where these chemicals were going, and what they were to be used for. Approving the sale of chemicals which can be converted into lethal weapons during a civil war is a very serious issue."
"We need to know who these chemicals were sold to, why they were sold, and whether the UK Government were aware that the chemicals could potentially be used for chemical weapons."
A government spokesman said: "The UK government operates one of the most rigorous arms export control regimes in the world, and has been at the forefront of implementing an international sanctions regime on Syria.
"In January 2012, we issued licences for sodium fluoride and potassium fluoride. The exporter and recipient company demonstrated that the chemicals were for a legitimate civilian end use - which was for metal finishing of aluminium profiles used in making aluminium showers and aluminium window frames.
"Before any of the chemicals were exported, the licences were revoked following a revision to the sanctions regime which came into force on June 17 2012."