Advertisers will be required to provide verifiable public contact details before they can run political campaigns on Facebook, the company has announced, in the latest attempt by the social network to increase accountability for so-called dark adverts.

The move is part of a raft of changes in the buildup to the European elections in May, when citizens from across the EU will vote in new MEPs.

Facebook’s political advertising restrictions will launch in the EU27 on Friday, following partial rollouts in six countries including the UK, US and India. The restrictions require advertisers on “political” topics – defined differently in each nation – to prove that they live in the country they are targeting, and to store all their adverts in a public database for seven years, along with information about targeting, spend and reach.

The rules require advertisers to disclose who “paid for” the advert, a requirement that has earned Facebook criticism in the past, since the company allowed users to write anything they wanted in the box and did not verify the names. Now, Facebook will continue to allow users to write what they want as the source of the funding, but will require they provide at least a phone number or email address through which interested parties can contact the advertiser. Users who advertise in a personal capacity will be free to not enter that information, but their name will be published instead, as verified by the site.

The requirement is retroactive, but Facebook will not be actively enforcing it for advertisers who have already registered unless users report them to the company for failure to provide further details. That includes campaigns such as Mainstream Network, which spent an estimated £250,000 on advertising to get Facebook users to urge their MPs to “chuck Chequers” and back a hard Brexit; and Britain’s Future, an obscure group that has spent more than £350,000 pushing for a hard Brexit since October.

The verification requirements will launch in all countries where the company operates its political advertising controls, including the US and UK. Advertisers in the EU27 will be able to register for verification from Friday, with verification becoming mandatory in mid-April, Facebook said. The process can move faster than it did in the UK and the US thanks to the widespread acceptance of national identification cards across the continent, which negates the need for a physical letter to be sent to verify residence. Advertisers will need to be verified separately in each EU country they want to run adverts in.

“We believe that more transparency will lead to increased accountability and responsibility over time – not just for Facebook, but for advertisers as well,” said Richard Allan, the head of global policy solutions at Facebook. Lord Allan is also a Liberal Democrat peer and a former MP for Sheffield Hallam, a seat in which he was succeeded by Nick Clegg, currently Facebook’s head of communications.

“We’re investing heavily in more people and better technology to proactively identify abuse,” Allan went on. “But if you see an ad which you believe is related to politics or issues and isn’t labelled, please report it. Facebook will review the ad, and if it falls under our political advertising policy, we’ll take it down and add it to the ad library.

“These changes will not prevent abuse entirely. We’re up against smart, creative and well-funded adversaries who change their tactics as we spot abuse. But we believe that they will help prevent future interference in elections on Facebook.”