The European Commission has again reiterated that the Brexit withdrawal agreement will not be negotiated, “full stop” – despite claims by Boris Johnson that he would somehow be able to reopen talks.

When asked whether the agreement could be reopened under any circumstances – including to stop a no deal or prevent a hard border in Ireland – a spokesperson for the commission was emphatic.

“I can confirm, as has been repeated several times, we will not be renegotiating the withdrawal agreement, full stop,” she told reporters in Brussels.

Asked to comment on what the view of Mr Johnson was within the EU institutions, the spokesperson said: “I would refrain from using any kind of adjectives to define any future prime minister of the United Kingdom and will repeat what we have said before, which is that the commission will work with any prime minister in the spirit of good cooperation.”

The frontrunner for Tory leader has said he would try to renegotiate the Brexit deal, and that the UK would be leaving the bloc on 31 October with or without an agreement. He has suggested he would withhold payment of the £39bn financial settlement if the EU did not agree to make changes to the treaty.

At a meeting of the European Council, Jean-Claude Juncker, the president of the European Commission, said all 27 EU leaders were “unanimous” that there should be no renegotiation of the deal, and that “nothing new” came out of discussions on it at the meeting. He had previously said the EU’s position was “crystal clear”.

EU leaders arriving at the summit in the EU capital on Thursday and Friday, which was mostly focused on other issues, such as choosing Mr Juncker’s successor and climate change, also presented a united front and said they would not renegotiate.

But the constant messages from Brussels stating they are not open to further talks do not appear to be getting through in Westminster, where practically all Tory leadership candidates suggested some kind of renegotiation. MPs rejected the deal as negotiated by Theresa May three times, precipitating her resignation.