The EU’s chief negotiator lobbied for the UK to be barred from stopping the article 50 process without the rest of the union’s consent, it has been claimed.

Senior Brussels sources say Michel Barnier asked for the line stopping the UK from unilaterally reversing the process to be included in a European parliament resolution that passed on Wednesday. The move came amid fears in Brussels that Theresa May could “abuse” the process to extend talks when the two-year negotiations are over. The European parliament’s resolution subsequently made clear the withdrawal process could only be stopped with the consent of the other 27 member states.

There are concerns among some in the EU that May could be tempted to revoke article 50 once it becomes evident that the two years allowed under the Lisbon treaty is insufficient time for the talks, only for her to then trigger the withdrawal clause once again, artificially extending the negotiating period.

The European commission believes that the EU treaties would not allow such a unilateral action. However, the alleged request from Barnier suggests some nervousness about what Britain would be prepared to do as the countdown begins on the two years of talks.

Campaigners, led by the barrister Jolyon Maugham, filed papers to the high court in Dublin earlier this week asking for the question of Britain’s ability to act unilaterally to be referred to the European court of justice. They want to empower the prime minister to revoke article 50 in the event of the House of Commons rejecting a poor deal when it comes in front of MPs in 2019.

The behind-the-scenes talks ahead of the European parliament’s resolution were revealed by Gianni Pittella, the leader of the socialist bloc, who told reporters at a dinner in Strasbourg that Barnier had asked for the wording on revocation, although a spokesman later said MEPs had always been in full agreement with the commission’s negotiator on the issue.

A second senior source in the European parliament claimed, however, that Barnier had been keen for the parliament to stress that the terms on which Britain could have a change of heart would have to be set by the other member states, if it was going to raise the issue of revocation in its resolution.

Asked about Barnier’s alleged request, a European commission source said: “Article 50 does not provide for the unilateral withdrawal of notification. In any dealings with the European parliament, Michel Barnier reiterated the above principle.”

Critics of the UK’s approach will see the move as evidence that the EU will have the upper hand. James McGrory, co-executive director of Open Britain, said: “This underlines what many suspect the government already knows: the idea of negotiating a complete deal in two years is a fantasy and a transitional deal is essential. A transition deal which protects our economy is going to require compromise on everything from payments to immigration to the ECJ.”

But others stressed that the government had no intention of revoking article 50. When May started the formal process, she told parliament: “This is an historic moment from which there can be no turning back. Britain is leaving the European Union.”

The European parliament resolution, passed last Wednesday, said: “A revocation of notification needs to be subject to conditions set by all EU27 [states] so they cannot be used as a procedural device or abused in an attempt to improve the actual terms of the United Kingdom’s membership.”

The motion is not legally binding, but as the European parliament has the right to veto any future deal between the UK and the EU, the clause on revocation sent a strong message about how the chamber expects the British government to behave.

Revoking article 50 would be an unlikely move by the prime minister, given the demand by some in her party that the UK leave the EU with or without a deal. The secretary of state for Brexit, David Davis, said earlier this year: “It is very difficult to see it being revoked. We do not intend to revoke it. It may not be revocable – I don’t know. That is the route we are going down.”

However, Lord Kerr, who drafted article 50, has previously said that he believes withdrawal can be unilaterally revoked. “During that period, if a country were to decide, ‘Actually we don’t want to leave after all,’ everybody would be very cross about it being a waste of time,” he said. “They might try to extract a political price, but legally they couldn’t insist that you leave.”