British firms supplied chemicals to Syria that were used to make the lethal nerve agent sarin, it has been claimed.

A statement will be published in the House of Commons today addressing historical exports to Syria, and a Government spokesman said controls have been tightened since the 1980s.

A leaked Foreign Office document said the phosphate chemicals used to manufacture sarin were supplied in the mid 1980s, according to claims made on the BBC Newsnight programme.

A report by the UN last year found that in one particular incident in Damascus "chemical weapons were used on a relatively large scale, resulting in numerous casualties, particularly among civilians and including many children".

While President Bashar al-Assad's government was accused of being behind chemical attacks during recent years of fighting, he has always denied this, blaming opposition forces.

Reacting to the Newsnight claims a Government spokesman said: "We do not comment on what are alleged leaked documents.

"Officials have been reviewing historical Government records on exports to Syria including from the 1980s, when we know Syria was building its chemical weapons programme and importing goods from a range of countries, with a view to an announcement in Parliament .

"Export controls have been tightened very significantly since the 1980s. We cannot though comment further before the Parliamentary written ministerial statement at 9.30am."

Newsnight claimed Ministers will confirm that UK firms provided the materials and that Syria has admitted they played a role in its chemical weapons programme.