The decision to allow UK firms to sell a chemical that can be used to make the deadly sarin nerve agent to Syria with Government permission needs to be investigated, a senior MP has said.
Supplies of sodium fluoride were exported between 2004 and 2010, during the build-up to the brutal civil war when Bashar Assad was believed to be stockpiling chemical weapons.
The substance is an ingredient of sarin, which UK experts have established was used in the attack on the outskirts of Damascus on August 21, in which the US says 1,429 people died, the Mail on Sunday reported.
The Department for Business, Innovation and Skills said there was "no evidence" the chemicals - which it licensed for export for use in cosmetics and healthcare - were diverted to weapons programmes.
"These licence applications, which predate the current conflict and EU sanctions, were rigorously assessed and determined to be for legitimate commercial use," a spokesman said.
The quantities involved were "commensurate with the stated end use", it said.
But the fact that such products were allowed to be exported at all has raised concerns and led to a call for an investigation by the House of Commons Committee on Arms Export Controls (CAEC).
Tory Richard Ottaway, who chairs the Foreign Affairs Select Committee, said: "Any sensible person would be concerned if an ingredient of sarin gas was exported from the UK to Syria.
"I think this is something for the committee."
The Department for Business, Innovation and Skills (Bis) granted a number of licences to specialist firms allowing them to deliver sodium fluoride to Syria before the current conflict and European Union (EU) sanctions.
Five were issued in July 2004, September 2005, March 2007, February 2009 and May 2010, the year before the civil conflict erupted.
Last week, UK scientists at Porton Down said they found positive evidence of sarin on samples of soil and clothing reportedly retrieved from the site of the attack.
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Professor Alastair Hay, a toxicology expert at Leeds University, told the Mail on Sunday: "The Government's approval of sodium fluoride sales to Syria during a period when it was widely suspected the regime was stockpiling dangerous substances is deeply disturbing.
"This was a serious mistake on Bis's part, as while sodium fluoride has a multitude of benign uses, such as toothpaste, it remains a key ingredient in the manufacture of sarin.
"Quite simply, you need fluoride to make sarin."
It comes after Bis admitted issuing licences for the export of sodium fluoride and potassium fluoride to the war-torn country in January last year before revoking them several months later.
The Government said no chemicals were exported before the licence - in that case for use in metal finishing - was revoked in June 2012 following EU sanctions.
Downing Street said that showed the system - which the Government claims to be "among the most stringent in the world" - was working.
Labour's Thomas Docherty, a member of the CAEC, said the "disturbing" revelations raised very serious questions for the committee.
"At no time should we have allowed president Assad's regime to get its hands on this substance," he told the newspaper.
"While the last export licence was issued in May 2010, these licences are obtained prior to manufacture and the industry standard is for four to five months to pass before the chemicals are delivered.
"So, we are looking at late 2010 for the British supplies of sodium fluoride reaching Syria. The Government has some very serious questions to answer," the MP said.
The revelations came as US secretary of state John Kerry was expected in the UK as part of a mission to drum up support for military action against the Assad regime in response to the deadly gas attack.
Videos of the aftermath of the episode - including images of children suffering the effects of nerve agent - are being distributed by the American administration in a bid to win backing in the US.
President Barack Obama is to address his nation on Tuesday as he seeks to win over a highly-sceptical public and political class ahead of votes in Congress to approve military action.
Kerry claims the number of countries willing to take part is now in double figures.
Foreign Secretary William Hague, who will hold talks with Kerry in the morning, denied the UK was "gung ho" for military action and recognised there was "a lot of public unease".
But he insisted the use of chemical weapons is "an evil we must stand up to one way or another".
Reacting to polls showing voters were widely opposed to military intervention in the wake of the 2003 Iraq war, he said: "Be reassured that we have learned lessons of Iraq.
"We are not seeking to be drawn into wars in the Middle East. We now make decisions in a completely different way," he said.
Ahead of his meeting with Kerry, he said: "They were disappointed with our vote, but we are a democracy, and therefore we respect the outcome.
"They are very understanding about that. They are very committed to what we call the special relationship.
"Britain has great and positive influence in the world, and we must make sure that we retain that. I am very determined, as the Prime Minister is, that we will not matter less," he told BBC1's Andrew Marr Show.
Speaking in Paris after meeting with Arab League nations, Kerry said "a number" of them had backed the call by a number of G20 countries for a "strong international response".
The UK was one of 11 of the world's biggest economies which released a joint statement blaming the Assad regime for the chemical attack after last week's summit in St Petersburg.
It has subsequently been endorsed by Germany.
But host Russia - one of Assad's staunchest allies - insists the attack was carried out by opposition forces and was among countries that did not sign up as the gathering highlighted stark divisions.
Kerry said: "We discussed the possible and necessary measures that the international community can take to deter Assad from ever crossing that line again.
"A number of countries immediately signed on to the G20 agreement that was reached by now 12 countries and they will make their own announcements in the next 24 hours about that."
He said: "What the United States is seeking - not alone but with others, an increasing number - is to enforce the standard with respect to the use of chemical weapons.
"We are not seeking to become engaged in or party to or take over Syria's civil war.
"All of us agreed, with not one dissenter, that Assad's deplorable use of chemical weapons, which we know killed hundreds of innocent people, including at least 426 children, on this occasion, this one occasion, crosses an international, a global red line."
As President Assad issued fresh denials of responsibility and warned of retaliation for any US-led strike, close regional ally Iran's new foreign minister declared that any use of force without UN authorisation would be illegal.
During a visit to Iraq, Mohammad Javad Zarif said: "I do not know why those who say all options are on the table do not understand the fact that civilised countries 65 years ago...rejected in the charter of the United Nations (the) resort to force as an illegal practice."