The EU will not renegotiate the Brexit deal that Prime Minister Theresa May agreed to, European Commission President Jean-Claude Juncker said on Tuesday.
Concerns are growing that a successor to the UK leader after her resignation could cause a confrontation with the bloc.
Brexit is up in the air after Mrs May’s announcement that she would step down, starting a leadership contest in the ruling Conservative Party.
The next prime minister could want a much more decisive break with the EU than that spelled out in Mrs May’s agreement.
One of the candidates, Foreign Secretary Jeremy Hunt, said it would be “political suicide” to pursue a no-deal Brexit.
It was a reprimand to front runner Boris Johnson, who said last week that Britain should leave with or without a deal by the end of October.
Mr Hunt, who voted to stay in the EU in the 2016 referendum but now accepts Brexit, said he would try for a new agreement that would take Britain out of the EU Customs union while “respecting legitimate concerns” around the Irish border.
But the EU was adamant that there would be no renegotiation.
“I will have a short meeting with Theresa May but I was crystal clear: there will be no renegotiation,” Mr Juncker said before a meeting of EU leaders in Brussels.
Irish Prime Minister Leo Varadkar said he believed the risk of Britain crashing out of the bloc without any divorce agreement was growing.
“I think there is a growing risk of a no deal,” Mr Varadkar said. “There’s a possibility that the new British prime minister may try to repudiate the withdrawal agreement.”
Any successor to Ms May will have to accept that the Brexit divorce deal she agreed to will not be ratified by the current British parliament, so a solution will have to be found for the Irish border issue that upset many MPs.
Many Brexit supporters opposed her deal because of a “backstop” that requires Britain to adopt some EU rules indefinitely, unless a future arrangement is found to keep open the land border between Northern Ireland and the Irish republic.
Under laws now in effect, Britain will automatically leave the EU on October 31 without an agreement unless Parliament approves one first, the EU grants an extension or the government revokes its decision to leave.
But Mr Hunt said any such move would be blocked by politicians and trigger a national election.
"Trying to deliver no deal through a general election is not a solution; it is political suicide," he wrote in the Daily Telegraph on Tuesday. "A different deal is, therefore, the only solution and what I will pursue if I am leader."
Trade Minister Liam Fox, who is not running for the premiership, said that while leaving with a deal was preferable, the leadership candidates agreed that exiting the EU without a deal was better than staying.
“If the EU doesn’t want to negotiate any changes, which I think would be unfortunate and quite surprising, then that does increase the chance of a no-deal exit,” Mr Fox said during a trade visit to Egypt.
Rivals for the top job were quick to reject Mr Hunt’s views.
“Political suicide actually lies in not having a clean break from the EU and not leaving on the October 31,” Esther McVey, a Brexit hardliner and former minister, said on Twitter.
Under the party’s rules for picking a new leader, Conservative members will compile a shortlist of candidates and put them to the party’s members for a vote. So far, 10 candidates have said they are running.
The Conservative Party had a disastrous showing in European elections at the weekend, losing most of its support to a new Brexit Party, which topped the poll while calling for a swift no-deal exit from the EU.
Other parties that want to halt Brexit altogether also surged in the vote, leaving little space in the middle for Britain’s two main traditional parties, the Conservatives and Labour, both of which had campaigned in favour of a compromise.
Labour has since said that a public vote, either a new national election or second referendum, is the way to reunite the country.
Several of Labour’s senior figures have called on its leadership to openly call for a new referendum in which the party would campaign to stay in the EU.