The UK will have to fight European elections, despite hopes from the government a Brexit deal would be done by then, says the PM’s de facto deputy.
The vote is due on 23 May, but Theresa May said the UK would not have to take part if MPs agreed a Brexit plan first.
Now, David Lidington says “regrettably” it is “not going to be possible to finish that process” before the date the UK legally has to take part.
He said the government would try to make the delay “as short as possible”.
The UK was due to leave the EU on 29 March, but as no deal was agreed by Parliament, the EU extended the deadline to 31 October.
It can leave the bloc earlier, but if the UK has not left by the 23 May, it is legally obliged to take part in the EU-wide poll and to send MEPs to Brussels.
The government has resumed talks with Labour to try to break the deadlock in Parliament over the terms of withdrawing from the EU. It has promised that if no compromise is reached, it will offer indicative votes on possible next steps to Parliament.
A number of other parties have already announced their candidates and launched their European election campaigns, but the Conservatives have yet to do the same.
The deadline to register for the EU elections is Tuesday 7 May.
Cabinet Office Minister Mr Lidington said: “Given how little time there is, it is regrettably not going to be possible to finish that process before the date that’s legally due for the European Parliamentary elections.
“We very much hoped that we would be able to get our exit sorted… so that those elections did not have to take place, but legally they do have to take place unless our withdrawal has been given legal effect.”
Mr Lidington said the government would be “redoubling efforts” in its talks with other parties to find a way forward to “make sure that the delay after [the elections] is as short as possible”.
And he said that “ideally” MEPs voted for by the UK would never have to take their seats in the European Parliament, as the session does not start until July.
“We would like to be in a situation… certainly to get this done and dusted by the summer recess,” he added.
By Chris Morris, BBC Reality Check
Even if an unexpected deal were to emerge in the next few days between the Conservatives and Labour, it would only be a very tentative first step towards Brexit, with no guarantee that it would enjoy a parliamentary majority.
And a first step isn’t enough.
The conclusions of last month’s EU summit, agreed by all EU leaders including Theresa May, said that if the Brexit withdrawal agreement has not been ratified in parliament by 22 May, the European elections will have to take place in the UK.
The ratification process means Parliament would have to pass a meaningful vote on the withdrawal agreement (the deal negotiated between the government and the EU), and then turn it into UK law in the form of a Withdrawal Agreement Bill.
And, as Mr Lidington has now conceded formally, time to do all of that has run out.
Some Brexiteers are angry at Mrs May’s efforts to find a compromise with Labour after her deal with the EU was effectively rejected by MPs three times.
One leading Eurosceptic, Sir Bill Cash, told the Press Association “the time has come” for the PM to resign and she “needs to be given a date”.
But Chancellor Philip Hammond defended the cross-party talks, suggesting the government had no other option.
Shadow chancellor John McDonnell said he was hoping to see “movement from government” when talks resume this afternoon.
He said they would go on “for the rest of this week, and then we’ll see where we’re at”.
Who is standing in the European elections?
The election in May will see 751 MEPs sent to the European Parliament to make laws and approve budgets for the EU.
Each country is allocated a set number of seats, depending on the size of its population.
The smallest member, Malta (population: around half a million) has six MEPs, while the largest, Germany (population: 82 million) has 96.
The UK is divided into 12 regions, each represented by between three and 10 MEPs depending on population size, ending with a total of 73.
Seats in England, Scotland and Wales are awarded to parties according to their share of the vote, then to the candidates on the lists drawn up by the parties.
Northern Ireland elects MEPs using a single transferable vote system, with voters able to rank candidates in order of preference.
Once the UK has left the EU, its seats will be divided up between the other 27 member states.