The chemical export licences were granted by Business Secretary Vince Cableâs Department for Business, Innovation and Skills last January -- 10 months after the Syrian uprising began.
They were only revoked six months later, when the European Union imposed tough sanctions on Assad's regime.
Yesterday, politicians and anti-arms trade campaigners urged Prime Minister David Cameron to explain why the licences were granted.
Dunfermline and West Fife Labour MP Thomas Docherty, who sits on the House of Commons' Committees on Arms Export Controls, plans to lodge Parliamentary questions tomorrow and write to Cable.
He said: "At best it has been negligent and at worst reckless to export material that could have been used to create chemical weapons.
"MPs will be horrified and furious that the UK Government has been allowing the sale of these ingredients to Syria.
"What the hell were they doing granting a licence in the first place?
"I would like to know what investigations have been carried out to establish if any of this material exported to Syria was subsequently used in the attacks on its own people."
The SNP's leader at Westminster, Angus Robertson MP, said: "I will be raising this in Parliament 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.
"The ongoing humanitarian crisis in Syria makes a full explanation around these shady deals even more important."
Mark Bitel of the Campaign Against Arms Trade (Scotland) said: "The UK Government claims to have an ethical policy on arms exports, but when it comes down to practice the reality is very different.
"The Government is hypocritical to talk about chemical weapons if it's granting licences to companies to export to regimes such as Syria.
"We saw David Cameron, in the wake of the Arab Spring, rushing off to the Middle East with arms companies to promote business."
Some details emerged in July of the UK's sale of the chemicals to Syria but the crucial dates of the exports were withheld.
The Government have refused to identify the licence holders or say whether the licences were issued to one or two companies.
The chemicals are in powder form and highly toxic. The licences specified that they should be used for making aluminium structures such as window frames.
Professor Alastair Hay, an expert in environmental toxicology at Leeds University, said: "They have a variety of industrial uses.
But when you're making a nerve agent, you attach a fluoride element and that's what gives it its toxic properties.
"Fluoride is key to making these munitions.
"Whether these elements were used by Syria to make nerve agents is something only subsequent investigation will reveal."
The Department for Business, Innovation and Skills said: âThe UK Government operates one of the most rigorous arms export control regimes in the world.
"An export licence would not be granted where we assess there is a clear risk the goods might be used for internal repression, provoke or prolong conflict within a country, be used aggressively against another country or risk our national security.
"When circumstances change or new information comes to light, we can -- and do -- revoke licences where the proposed export is no longer consistent with the criteria."
Assad's regime have denied blame for the nerve gas attack, saying the accusations are "full of lies". They have pointed the finger at rebels.
UN weapons inspectors investigating the atrocity left Damascus just before dawn yesterday and crossed into Lebanon after gathering evidence for four days.
They are now travelling to the Dutch HQ of the Organisation for the Prevention of Chemical Weapons.
It could take up to two weeks for the results of tests on samples taken from victims of the attack, as well as from water, soil and shrapnel, to be revealed.
On Thursday night, Cameron referred to a Joint Intelligence Committee report on Assad's use of chemical weapons as he tried in vain to persuade MPs to back military action. The report said the regime had used chemical weapons at least 14 times since last year.
Russian president Vladimir Putin yesterday attacked America's stance and urged Obama to show evidence to the UN that Assad's regime was guilty.
Russia and Iran are Syria's staunchest allies. The Russians have given arms and military backing to Assad during the civil war which has claimed more than 100,000 lives.
Putin said it would be "utter nonsense" for Syria to provoke opponents and spark military retaliation from the West by using chemical weapons.
But the White House, backed by the French government, remain convinced of Assad's guilt, and Obama proposes "limited, narrow" military action to punish the regime.
He has the power to order a strike, but last night said he would seek approval from Congress.
Obama called the chemical attack "an assault on human dignity" and said: "We are prepared to strike whenever we choose."
He added: "Our capacity to execute this mission is not time-sensitive. It will be effective tomorrow, or next week, or one month from now.
"And Iâm prepared to give that order."
Some fear an attack on Syria will spark retaliation against US allies in the region, such
as Jordan, Turkey and Israel.
General Lord Dannatt, the former head of the British Army, described the Commons vote as a "victory for common sense and democracy."
He added that the "drumbeat for war" had dwindled among the British public in recent days.