Brexit negotiations have hit their most difficult stage, with Brussels still unsure whether a deal with Boris Johnson is possible within the next two crucial weeks, the European council president, Charles Michel, has said. The former prime minister of Belgium, who leads the summit of EU leaders, said in an interview with the Guardian that the result still was still hanging in the balance with what he suggested was a further fortnight of talks to come. The EU’s chief negotiator, Michel Barnier, is expected to stay with his team in Westminster until Thursday, after which the troubled negotiations are due to resume in the Belgian capital. Both sides are seeking to keep outside commentary on the negotiation to a minimum in a sign that the talks have effectively entered a so-called “tunnel” or “submarine” phase, where the negotiators seek to hash out the final details away from the glare of the media and domestic political stakeholders. But Michel said Barnier was still maintaining a flow of intelligence to the member states, in preparation for a deal being struck and ratified. He conceded that it was as yet too early to say whether there would be a successful outcome from the final decisive phase. “In my opinion it’s very clear that it is necessary to work seriously, [which is] what we are trying to do, with full trust for Michel Barnier and his team, and we will assess in the next days or in the next weeks, when we consider it is time to assess, what is the result of the talks that are ongoing.” Michel said. “We all know that in all negotiations, the last and final decisions are the most difficult. Will we get a deal? I don’t know, it will depend on what will be on the table. But we are working in order to make sure all member states are well informed, are involved in the process in order to make sure there is confidence – which is key in order to able to decide.” The outstanding issues in the trade and security talks remain the level of access to British waters provided to foreign fishing fleets, fair competition rules for business, including rules on domestic subsidies, and mechanisms in the final treaty for resolving future disputes. “It is not a surprise. You know what are the most difficult topics, and we are working to try to find solutions on the most difficult topics,” Michel said. “It’s not possible for me to assess what will happen in the next days or in the next two weeks.” EU sources have suggested that mid-November is now the absolute deadline for a deal in order for there to be time for parliamentary ratification on both sides of the Channel. Michel was speaking to a group of European newspapers before a videoconference meeting of EU leaders on Thursday where the 27 heads of state and government will seek to further coordinate their efforts in tackling the coronavirus pandemic. Michel said there needed to be a unified approach to both the use of rapid testing kits and the rollout of a vaccine. He said he expected at least one of the vaccines currently under trial to be available by the end of the year, albeit there could be no certainty. “We need to speak the truth,” Michel said. “The current situation in Europe is serious and bad. That’s why we need to act and it is urgent … I remember that before the summer we thought there was a risk, without certainty, that we would face the second wave after the summer. And now, no doubt, there is a second wave, [a] strong second wave.”