Facebook and its new head of global affairs, Nick Clegg, stand accused by Brussels of taking a “patchy, opaque, and self-selecting” approach to tackling disinformation.

The description was said to apply to a number of internet companies by the EU commissioner, Sir Julian King, at the publication of a progress report on the attempt to clamp down on fake news before May’s European elections.

But it was Mark Zuckerberg’s company, one of four major signatories to a new code of conduct, which bore the heaviest criticism from senior officials in the EU’s executive branch during a press conference in Brussels.

Asked about the appointment of Clegg, the former British deputy prime minister, as Facebook’s head of global affairs, King said: “I wish Nick Clegg well, I wish him luck. I think he is going to need it.”

On Tuesday, the commission published the first reports submitted by Google, the web browser Firefox Mozilla, and the social media platforms Facebook and Twitter on their adherence to the voluntary code of practice signed in October.

Under the code, the internet firms are obliged to disrupt revenue for accounts and websites misrepresenting information, clamp down on fake accounts and bots, give prominence to reliable sources of news and improve the transparency of funding of political advertising.

Clegg, who worked for the European commission in the mid-1990s, announced on Monday, during a visit to the Belgian capital, that Facebook would tackle political misinformation in the run-up to the EU elections with a “war room” based in Dublin.

But while King said the development was welcome, he expressed his evident frustration with Clegg’s Silicon Valley employer.

“Allow me to thank Facebook for their announcement yesterday of strengthened efforts to tackle disinformation, including more transparent political advertising, more resources for rapid response, and boosting their capacity to fight fake news”, said King.

“Ideally it would have been even better if they had been able to report on these measures to us as part of this reporting process. Ideally they would have provided figures breaking down their performance against the performance indicators for the last quarter of last year. We look forward to them doing that.”

King complained that independent researchers had not been allowed access to Facebook’s data, “and we need to do something about that”. He noted that by the firm’s own figures the site still hosted “80 to 90m” fake accounts.

“Facebook is working with third-party fact-checkers and that is great,” he said. “But they are doing it in seven member states. We need to do it in all member states.”

Of the other tech companies, Google was said to be “making progress” in scrutinising the placement of adverts, fighting fake accounts and impostor websites.

But the commission said that tools to prioritise reputable news outlets were available only in a small number of member states

Twitter was said to have drawn up new measures designed to act against malicious actors on its platform and automated systems or bots. But the commission said the company had not shown how it was ensuring that its advertising service blocked such accounts from promoting their tweets.

Mozilla Firefox is upgrading in order to limit the information it revealed about users’ browsing activity but the commission said it was seeking further details on its rollout across the EU.

King said: “Time is of the essence. There are lot of measures that need to be in place before the elections but the pre-election campaigns have already begun in many countries so we need to speed up these measures.”

The tech companies are expected to update the commission on progress against the code of conduct every month for the next 12 months or risk the imposition of regulation.

There is growing anxiety that the elections to the European parliament could be the target of manipulation in a similar manner to the US presidential election and the UK’s Brexit referendum.

King said: “We remain concerned about the pace of progress. The pace of progress on these issues needs to be faster. We can’t afford to wake up after the election to find we could and should have done more. We need to take action now.”