IT was famously started by founder Mark Zuckerberg as a 19-year-old student at Harvard University as a means of helping fellow students stay in touch. Now the reach of Facebook is truly staggering with around two billion people – more than one-quarter of the world’s population – signed up to the site.

But while users happily post about everything from their job, favourite places to visit and family and friends, there are increasing questions being raised over the use of information gathered by the site’s closely-guarded computer algorithms to target voters during elections.

Political campaigns can now send out carefully-tailored messages based on an individual’s interests, location, age, gender and other personal factors.

Last week, it was reported that during the Brexit campaign pro-Leave groups spent nearly £4.7million with a web analytics company called AggregateIQ to target voters with personalised adverts.

An investigation by BBC Panorama also revealed how Facebook was seen as key to Donald Trump’s victory in the US elections and the vote to leave the EU, according to those who ran the campaigns.

Gary Coby, of the Republican National Committee, told the programme the “way we bought media on Facebook was like no-one else in politics has ever done”.

He described how they sent information such as names, addresses and emails to Facebook, who would then match it to user profiles and group people into "buckets" to be targeted.

Gerry Gunster, campaign strategist at Leave.EU, said there was no question Facebook had been a “game changer” for the campaign. He said: “You can say to Facebook, I would like to make sure I can micro-target that fishermen in certain parts of the UK, so that they are specifically hearing on Facebook that if you vote to Leave, that you will be able to change the way the regulations are set for the fishing industry.”

Dr Mark Shephard, a senior politics lecturer at the University of Strathclyde in Glasgow, said he was concerned about the use of algorithms in social media feeds.

“If we are searching for certain things, eventually we will get typecast as a certain type of person with the information we receive,” he said. “I find that a little bit disturbing.”

He added: “It is important to get people to force themselves to visit all the different parties’ websites and not to just read what you want to hear or be told to read about one thing. Just be open to what is out there and make your mind up as best you possibly can.

"In an ideal world people would read the party’s manifestos, they would cross-check the information they receive, and then they would make a best judgement

“I am a little bit worried people are being targeted with stories – in a way it is quite divisive, as if you are getting people to constantly confirm their pre-existing bias, therefore you are moving people further and further apart.”

There have been claims that the influence of Facebook is now such that it will play a decisive role in the forthcoming General Election.

One group, Who Targets Me?, is hoping to find out more about how political advertising on Facebook will play a part by launching a plug-in web browser which tracks adverts on a user’s feed. Anyone who installs it will be able to find out information on how they are being targeted by different political parties, with the data also gathered on nationwide basis to show wider trends.

Sam Jeffers, co-founder, said: “Targeted advertising in this way is a fairly new thing in this election. One of the things we are hoping to do is increase transparency and accountability about it, to help people know essentially why they are being targeted and to track national trends a bit better. There is also a need to look at the content of some of those ads, as unlike in an election leaflet, no physical thing exists.

“The ads are quite ephemeral and they come and go, so we are hoping to track a fairly large proportion of the content the parties are putting out and paying money to promote.”

However, Jeffers said he believed there were some “wild claims” being made about the power of Facebook to influence individual voters and the project aimed to find out exactly how sophisticated the targeted messages were.

“There is scope for research after this to answer questions such as does Facebook actually matter – and what type of influence we want money and targeted advertising to have in our election?” he added.