What is purdah? EU referendum political 'blackout' explained ahead of spending limits vote

Ahead of Britain's planned referendum on their membership of the EU, David Cameron is facing his first major backlash over plans to scrap spending limits ahead of the poll.

Cameron is facing a rebellion from as many as 50 of his own backbenchers over his plans to scrap the period known as "purdah" in the weeks before the referendum in 2017.

The prime minister is hoping to lift purdah rules ahead of the EU referendum, which effectively bans the government, civil servants and other bodies from making announcements and limits spending in the run up to an election result.

This period, where local and central government cannot make any new announcements or legislative changes, is put in place so government departments cannot release any official statements that might give an unfair advantage to either side.

The word purdah derives from the Persian word "pardeh" meaning curtain or veil and was traditional used to describe the "hiding" of women's modesty from men. In modern political terms, it has taken a second meaning for the hiding of government initiatives or legislation for a period.

Purdah usually comes into force six weeks before the result of a general election. For the 2015 general election, purdah became effective after parliament dissolved on 30 March and remained in place until 7 May. The time period was also put in place 28 days prior to the Scottish referendum in 2014.

In 2010, there was a purdah enforced for social media for the very first time. The Cabinet Office warned government departments to only use Twitter for "publishing factual information only in line with guidance on news media" while during the purdah period.

MPs are now set to vote on to pass the amendment allowing a relaxation of the purdah rules ahead of the EU referendum.

Cameron could see his first "bloody nose" in the House of Commons if MPs vote to whether to keep the changes.

Foreign Secretary Philip Hammond believes it would be "unworkable and inappropriate" to impose purdah for an EU referendum. Owen Paterson, the former environment secretary, is one of those who has publicly spoken out against not suspending ministerial activity in the run up to the historic poll, describing it as "unacceptable".

Former SNP leader Alex Salmond also said the government could attempt to "rig" the referendum result if purdah is not enforced in the weeks prior to the result.