It’s polling day. A day ripe for conspiracy theories. Particularly about pencils. Take your own pen to the ballot box, suspicious voters say, because otherwise your vote could be erased by MI5.

This is summed up by the #usepens hashtag on Twitter, warning against using a polling booth pencil.

According to YouGov, 28 per cent of people believe that the EU referendum will be rigged. The percentage increases to almost half (46 per cent) among Leave voters. And 28 per cent of Leave supporters suspect the pro-EU involvement of the secret services (that MI5 is working with the government to stop Brexit), while 16 per cent of Remain backers are also wary of the involvement of security services.

#TakeBackControl of your vote today. Bring with you a pen to vote, don't use a pencil, and of course #VoteLeave pic.twitter.com/XUoP7UxF7a — Tommaso Papini (@TmsPapini) June 23, 2016

Police were even called to a polling station in Chichester today to question a Brexit supporter handing pens out to voters.

But there are many reasons why polling booths provide pencils rather than pens. They’re cheap, they don’t run out of ink, they make a mark first time, and they’re easier to read for the tellers than thinner pen marks.

Also, the pencils used are a particular type that don’t smudge and are difficult to rub out, while pens are more likely to run or smudge if they get wet, or when the ballot paper is folded. It is also less likely that people will be able to graffiti polling booths with pencils.

Please use a pencil on your ballot paper as ink can smudge when its folded which could make the paper doubtful & it may not be counted — EastNorthantsCouncil (@ENCouncil) June 23, 2016

Anyway, you are allowed to use your own pen or the pencils provided. It’s up to you. And campaigners can go and observe the count, to ensure no one shady is taking to the ballot papers with an eraser.