BRUSSELS (Reuters) - European Union officials are considering an extension of the EU commission’s mandate should Britain be granted a long delay to its planned exit date, a senior official said on Wednesday.

It was a further sign of how Brexit delays could upset the functioning of the European Union.

EU leaders were set to grant Prime Minister Theresa May a second postponement to Britain’s fraught exit at an emergency summit on Wednesday but were expected to argue over how long and on what terms.

A Brexit delay beyond EU Parliament elections scheduled on May 23-26 would force Britain to participate in the vote and elect representatives to the EU assembly - an option May wants to avoid but which could become inevitable if the British parliament fails to ratify a withdrawal deal in coming weeks.

British participation could change the political balance in the next European legislature, EU officials fear, as Britons are seen electing strongly euroskeptic lawmakers, boosting already growing numbers of nationalists who seek to weaken the bloc.

Yet Britain’s Labour Party, if it fields candidates, could boost the weight of the socialist grouping in the EU assembly, potentially allowing the center-left to gain a majority.

Polls in the remaining 27 EU countries currently predict the center-right will win most seats in the next EU parliament - so when Britain and its deputies leave the EU, the majority in the European assembly could change.

That raises uncertainty over the next executive commission, which must be approved by European lawmakers. As a result, EU officials are considering extending the mandate of the existing executive led by Jean-Claude Juncker beyond its term which expires at end of October, the senior official said.

This extension, which would be limited to a few months, would avoid the risk that a changed power balance in the EU parliament after Brexit could raise doubt about the legitimacy of the new executive, the official said.

Commission Vice-President Frans Timmermans said on Wednesday he saw no reason to extend its mandate. He is the candidate for the socialist grouping for the presidency of the new commission.

Britain’s May has asked for a delay of Brexit until June 30. EU summit chair Donald Tusk favored a longer, flexible extension of up to 12 months. France and Germany supported a shorter extension.

Conditions to limit Britain’s role in the EU during any Brexit extension period in the coming months were expected to be agreed at Wednesday’s EU summit.