Former European commission president says constructive negotiations between EU and UK leaders are needed to reach a deal

Brexit negotiations are on course to fail unless both Britain and the European Union ditch their winner-takes-all approach to the coming talks, the former president of the European commission José Manuel Barroso has said.

With just days to go before Theresa May formally notifies Brussels of the UK’s intention to leave the EU, Jean-Claude Juncker’s predecessor said the two sides were playing a dangerous game.

The UK’s prime minister has said she believes “no deal is better than a bad deal”, and some in her cabinet have openly talked up the prospect of walking away from the negotiating table.

Michel Barnier, the EU’s chief negotiator, has placed the settlement of Britain’s £50bn in financial liabilities as the prerequisite for any progress. Last week the French former minister conjured up a vision of queues of Dover, nuclear fuel shortages and chaos for citizens as a consequence of Britain’s failure to live up to its responsibility.

Asked about the coming Brexit talks on the margins of Saturday’s Rome summit to mark the 60th anniversary of the EU’s founding, the French president, François Hollande, he said he wanted them to be amicable but added: “We will ensure that it does not happen to Europe’s detriment, that Britain remains a partner of the union but that, necessarily, it will pay the consequences.”

Barroso also suggested that extremists on both sides of the Channel wanted the UK to break away from the EU entirely.

“I think both sides until now mostly put the issue in terms of a zero-sum game and I think this is not helpful,” he said.

“What they should understand, both sides, is that we have to work constructively because, whether some people like it or not, Britain will be part of Europe. Some people both on the continent and in the UK don’t like the idea that Britain is part of Europe, but it is.

“Of course, Britain not keeping the responsibility of membership cannot expect the privileges of membership, that’s quite clear. Having said that, I think it is possible to come to a constructive agreement that minimises the negative points and offers some way forward. But that requires on both sides strategic thinking and leadership.”

Barroso spoke ahead of the publication of a report on Monday from the organisation that represents British manufacturers, the EEF, saying it would be unacceptable for the British government to come away without a deal.

About 52% of all UK manufactured exports by value went to the EU in the 12 months to April 2016, with production processes crossing European borders numerous times.

Estimates in the chemicals sector have shown that a tariff of between 4% and 6% tariff, which the EU imposes on non-member states, would increase direct trading costs by more than £50m for a single company.

The EEF will say that if the UK walk away with no preferential access to the EU market in place, the manufacturing sector would bear much of the brunt of an immediate financial loss.