Digital campaign experts have created program to allow voters to expose how political messages arrive in Facebook feeds

A tool exposing how voters are targeted with tailored propaganda on Facebook has been launched in response to what is likely to be the most extensive social media campaign in general election history.

Experts in digital campaigning, including an adviser to Labour in 2015, have designed a program to allow voters to shine a light into what they describe as “a dark, unregulated corner of our political campaigns”.

The free software, called Who Targets Me?, can be added to a Google Chrome browser and will allow voters to track how the main parties insert political messages into their Facebook feeds calibrated to appeal on the basis of personal information they have already made public online.

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It aims to show who campaigns are targeting, how much the parties are spending and will shed light on whether targeted adverts are crossing the boundary into “fake news”. The creators hope thousands of people will sign up.

It comes as both Conservatives and Labour plan extensive Facebook campaigns ahead of the 8 June poll. The Conservatives have rehired Craig Elder and Tom Edmonds, the digital consultants who worked on the 2015 election battle, in which the party spent £1.2m spent on digital campaigning, against Labour’s £160,000. This time, Labour is understood to be ready to spend around £1m.

Elder and Edmonds last year worked for Britain Stronger In Europe, the designated remain campaign in the EU referendum. In one instance, they targeted Facebook users who had expressed strong support for a Premier League team through “likes” with a post about the impact on their side of foreign players needing visas in the event of Brexit. People who had mentioned they liked surfing would receive a message about the value of EU regulations on beach pollution.

Andrew Gwynne MP, Labour’s campaign co-ordinator, has said targeted Facebook advertising will have a “significant impact” on the election. Labour will use a new system called Promote to identify specific people in a constituency at whom candidates will be able to target a message.

“For the good of our democracy, it’s time to throw some light on this dark and unregulated area of campaign spending,” said Sam Jeffers, who has helped to devise the software, which is available as a browser extension.

“Facebook advertising is highly targeted and tailored to the recipient, battle-tested for effectiveness, yet invisible to anyone but the end user. There are no spending limits on digital ads, despite strict legal controls in other areas of campaign expenditure. It gives big money a strong voice in our elections.”

The Electoral Commission, which regulates campaign spending, told the Guardian it would be carefully considering the use of social media over the coming six weeks. “Even after 2015 it has expanded so much,” a spokesman said. “We want to make clear how greater clarity can be provided to voters.”

Instead of parties simply declaring an overall amount spent on Facebook, it wants them to provide details on dates and topics covered in adverts.

Political Facebook ads emerged as a key tactic during the 2016 EU referendum. The official Vote Leave campaign pumped out about 1bn targeted digital adverts, mostly via Facebook. Vote Leave’s campaign director, Dominic Cummings, has claimed it spent 98% of its £6.8m budget on digital.

It remains unclear how Arron Banks, the millionaire backer of the Leave.EU campaign, may deploy his social media team, which is based in his Bristol insurance company HQ and was schooled in political campaigning with guidance from Cambridge Analytica, a Washington-based firm partly owned by Donald Trump donor Robert Mercer.

Leave.EU is currently under investigation by the Electoral Commission over whether it received any impermissible donations and whether its spending return was complete. Banks has denied breaching any electoral law.

“We can use this information to help people understand why they’re seeing specific messages,” said Jeffers. “We might also be able to use the data to work out whether campaigns are operating within the law. For example, are they respecting national v constituency spending limits? Are they discriminating against a particular group of the population?”

The Electoral Commission said that if a post promotes a candidate it must be accounted as constituency spending, which typically has a £15,000 limit. If it deals with broad party policy, it should be accounted nationally.

This was not as sophisticated as the “psychographic” techniques claimed by Cambridge Analytica. Its British chief executive, Alexander Nix, has said it gathers voters’ social media data and ranks them according to openness, conscientiousness, extroversion, agreeableness (including whether you put others’ needs and society ahead of yourself) and neuroticism.

In a conference presentation, Nix gave the example of a campaign supporting the right to gun ownership: “For a highly neurotic and conscientious audience you are going to need a message that is rational and fear-based,” he said. That could lead to an image of a burglar’s hand smashing a window and a slogan about the second amendment being an insurance policy. For a closed and agreeable audience that cares about family and tradition, the slogan might be: “From father to son, since the birth of our nation” would work better.