An anti-Brexit protester holds up a sign outside the Houses of Parliament in London, Britain March 14, 2019. REUTERS/Dylan Martinez

BRUSSELS (Reuters) - The European Union executive said Britain will have to justify any request to postpone Brexit beyond the end of this month and that EU leaders would put a priority on avoiding disrupting EU institutions in considering it.

Noting Thursday’s votes in the British parliament to seek a delay in leaving the bloc, a spokesman for the European Commission said: “A request for an extension of Article 50 requires the unanimous agreement of all 27 member states.”

The Council of national leaders, he said, would “consider such a request, giving priority to the need to ensure the functioning of the EU institutions and taking into account the reasons for and duration of a possible extension.”

The Council is due to meet next Thursday and Friday. Several leaders have already said that Britain must either have left before a new European Parliament is elected in May to take office in July or must hold its own EU election in order to avoid any legal challenge to the legitimacy of the legislature.

Some have also said that Britain should not be allowed merely to continue to remain a member while giving no clear indication of what it planned to use an extension for after months of deadlock in London over whether or not to accept a Brexit treaty agreed by Prime Minister Theresa May.