Problems that denied EU citizens their vote in last month’s European elections were evident five years ago, according to a leaked letter from the European commission.

Many EU nationals were unable to vote in the European elections on 23 May, through a series of bureaucratic muddles and mistakes that experts decried as a fiasco that a democracy should not tolerate.

A letter sent on Friday to the constitution minister, Chloe Smith, shows that some of the chaos at polling stations was foreshadowed in previous European elections in 2014.

“The commission notes that the difficulties encountered were largely recurrences of the incidents and deficiencies that had previously arisen during the 2014 elections and which the United Kingdom had undertaken to remedy in time,” states a copy of the letter seen by the Guardian.

The government told the commission in January 2015 that it would remedy the problems identified in 2014, either through legislation or practicalities before the 2019 vote.

The letter, from the EU justice commissioner, Vĕra Jourová, acknowledged that British authorities faced “practical challenges” because of the last-minute Brexit delay, but concluded this should not have affected “the obligation of the United Kingdom to respect the right to vote of EU citizens”.

Theresa May said she did not want the UK to participate in European elections, even after agreeing a six-month Brexit extension with the EU on 11 April. The prime minister still thought it possible to get her deal through parliament and avoid the EU-wide vote. She also said the government was making “responsible preparations” to hold the elections.

The commission identified four main bureaucratic problems encountered by EU nationals in the UK: councils failed to inform EU citizens about the two-step registration process; councils did not send out forms on time to people who requested them; or forms were not registered despite being sent. Finally, the letter states, staff at polling stations “failed in many cases to adequately respond to EU citizens’ complaints” after they were unable to vote, despite taking all the necessary steps.

The government has been asked to send the commission data about complaints. EU authorities also want to know how the government attempted to tackle the problems first identified in 2014.

The UK has been given 10 weeks to draw up a response – a late September deadline that falls just one month before Brexit day on 31 October.

Usually, persistent rule-breaking governments are taken to the European court of justice. The looming Brexit deadline makes any legal action politically charged for the commission.

A government spokesperson said: “The UK government took all the legal steps necessary to prepare for the European parliament elections, including putting in place all the necessary legislative and funding elements to enable returning officers to make their preparations required for the polls on 23 May.

“We worked with returning officers, the Electoral Commission and other agencies such as the Society of Local Authority Chief Executives (Solace) and the Association of Electoral Administrators (AEA) to support the smooth running of the polls.”