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Boris Johnson is set to meet German Chancellor Angela Merkel in Berlin later, where he is expected to reiterate his call for the backstop plan to be scrapped.
The PM has said the arrangement to avoid a hard border in Northern Ireland is “anti-democratic” and must be removed to secure a Brexit deal.
But the EU has rejected the possibility of any changes to the backstop.
Mr Johnson said the EU’s response to his demands was “a bit negative”.
However he said he would enter Brexit talks with “a lot of oomph” and there was “a real sense that something needs to be done” with the backstop.
“We can’t get it through Parliament as it is,” he added.
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Mr Johnson is also expected to tell Ms Merkel the EU should not make the mistake of believing Parliament could somehow block the UK from leaving on the 31 October deadline.
The prime minister will also reiterate that, while he wants a deal, if the EU is not willing to negotiate the UK will still be leaving at the end of October.
Speaking ahead of the meeting, Ms Merkel said a solution could be found to the Irish border issue that meant the backstop would not be needed – but indicated there would be no change to the withdrawal agreement.
Mr Johnson’s meeting with the German chancellor is the first in a series of talks with EU leaders.
On Thursday, Mr Johnson will travel to Paris to meet French President Emmanuel Macron and on Saturday he will attend the G7 summit alongside other world leaders including US President Donald Trump.
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In a letter to European Council President Donald Tusk on Monday, Mr Johnson said the backstop – which is part of the withdrawal agreement negotiated by former prime minister Theresa May – risked undermining the Northern Irish peace process.
The deal has been rejected by Parliament three times and Mr Johnson argued it would not be passed by MPs unless the backstop was removed.
The Irish border is a matter of great political, security and diplomatic sensitivity, and both the UK and EU agree that whatever happens after Brexit there should be no new physical checks or infrastructure at the frontier.
The backstop is a position of last resort to guarantee that, but if implemented, it would see Northern Ireland stay aligned to some rules of the EU single market.