Boris Johnson will travel to Brussels for a face-to-face summit with the European commission president, Ursula von der Leyen, in an 11th-hour attempt to break the impasse in the Brexit negotiations. A long-awaited crunch meeting will be held in the “coming days”, the two leaders said in a joint statement following a phone call lasting over an hour, keeping hopes alive of agreement on a trade and security deal. Sources on both sides pointed to Wednesday or Thursday as the most likely dates. Both EU and UK insiders said there was no certainty that a historic trade and security deal would be secured when the leaders meet, however. “Talks are in the same position now as they were on Friday,” a UK government source said. “We have made no tangible progress. It’s clear this must now continue politically. Whilst we do not consider this process to be closed, things are looking very tricky and there’s every chance we are not going to get there.” One senior EU diplomat added: “We shall light a candle for them.” The joint statement from Johnson and Von der Leyen came hours after Britain said in the event of a deal it would drop key clauses from the internal market bill that would breach international law by letting the UK unilaterally rewrite parts of the Brexit departure agreement. The move was seen as an olive branch to the EU. It is now just over three weeks from the end of the Brexit transition period, when the UK leaves the single market and customs union with or without an agreement. Chief negotiators are still struggling to find common ground on the thorniest issues despite nine months of talks. Ireland’s foreign minister, Simon Coveney, said there would need to be a major change in the British approach for the upcoming summit to be a success. “The next two days need to be very different to the last two days,” he said. “In Brussels certainly the mood is starting to shift to contingency planning for a no deal, as opposed to the compromises that are necessary to get a deal done. That is not where we want this to go.” During the call with Von der Leyen, the prime minister outlined his difficulties with EU demands on issues ranging from fisheries to provisions on fair competition. After more than an hour, he asked for a break to confirm with his aides, including his chief negotiator David Frost, that there were sufficient grounds to make the trip to Brussels. EU sources said there had been no need for him make a second call to Von der Leyen to discuss an alternative plan as Downing Street was in agreement on a statement announcing the make-or-break summit. “We agreed that the conditions for finalising an agreement are not there due to the remaining significant differences on three critical issues: level playing field, governance and fisheries,” the leaders said. “We asked our chief negotiators and their teams to prepare an overview of the remaining differences to be discussed in a physical meeting in Brussels in the coming days.” Earlier in the day the EU’s chief negotiator, Michel Barnier, had told MEPs the talks were “not far from the very endgame”, warning he would not continue beyond Wednesday. Both sides will need time to ratify any agreement. Downing Street has said it will hold a vote on new legislation overriding the withdrawal agreement on Wednesday – a potentially deal-breaking move. EU leaders will meet on Thursday, when they could sign off on an agreement or trigger their preparations for a no-deal outcome, including temporary legislation to keep planes in the air. A senior EU diplomat said: “The outcome is still uncertain, it can still go both ways. The EU is ready to go the extra mile to agree on a fair, sustainable and balanced deal for citizens in the EU and UK. It is for the UK to choose between such a positive outcome or a no-deal outcome.” Difficulties remain in agreeing terms on EU access to British fishing waters, provisions to ensure fair competition and a system of dispute resolution if the terms of the treaty are breached. Tentative progress on the issue of EU fleets’ access to British fishing waters, as reported by the Guardian, was upended late on Sunday night when Frost is understood to have tabled new demands about the ownership of vessels in British seas. Under the proposals, any foreign majority-owned vessels would not be allowed to sail under the UK flag, sources in Brussels said. Vessels currently need only an “economic link” to the UK, such as landing more than half their catch at British ports or having majority British crews. Companies based in Iceland, Spain and the Netherlands fished 55% of the UK’s fishing quota by value in 2019, according to BBC research published this year. One EU diplomat said: “This has really caused a lot of problems. A paper was handed over late on Sunday night. This is serious.” Barnier said there also remained differences over fishing quota numbers and the UK’s intention to block access to the six- to 12-mile zone, seas in which French and Belgian fleets in particular have fished for centuries. “That is worrying at this stage in the negotiation,” he said. On the so-called level playing field clauses in the treaty, Barnier said the issue of “non-regression” from current standards had progressed well but that common ground had still not been found on the EU’s demand for a “ratchet clause”. The provision would ensure a baseline of minimum environmental, social and labour standards raises on both sides over time. The issue was fast becoming the biggest obstacle to a deal, EU diplomats said. Barnier told ambassadors he was optimistic that an agreement would fall into place on dispute resolution where either side breaches the terms of the deal. Downing Street was yet to agree to provisions that would allow for one side to suspend parts of the deal, known as a “cross suspension clause”, but Barnier said he was confident about finding a solution. It came as Brexiter Tory MPs in the influential European Research Group (ERG) said they would study carefully the text of any agreement reached with the EU. Former party leader Iain Duncan Smith told MPs in an emergency Commons debate on the talks that “the British public voted for a sovereign departure” in a series of coordinated interventions. Veteran Brexiter Peter Bone said he was confident that Johnson would bring back a deal that “takes back control of our laws, borders and trade”, adding: “I bet my house on it that he will not betray those principles.” Particular concern on the party’s right was also expressed about the “ratchet clause” but the ERG is likely to take legal advice and carefully study the deal to see if they believe the UK’s freedom of action is impacted. A hard core of two to three dozen rebels would be ready to vote against a deal in such circumstances, which would be embarrassing for the prime minister who has drawn support from the ERG, but not fatal to a deal being ratified.