The EU’s chief Brexit negotiator, Michel Barnier, has challenged Theresa May’s beleaguered government to address the fundamental question of whether Britain wants to deregulate and follow the US social and economic model or stay within the European mainstream.

Speaking in Rome, Barnier voiced his concern over recent comments by the US commerce secretary on a visit to London, with whom the trade secretary, Liam Fox, is in discussions over a future trade deal.

“When I hear the US secretary of commerce, Wilbur Ross call, in London for the British to diverge with Europe to better converge towards others – towards less regulation, environmental, sanitary, food, probably also financial, fiscal and social – I’m wondering”, Barnier said. “The United Kingdom has chosen to leave the European Union. Will it also want to move away from the European model? That’s another question.

“There is behind this European regulatory framework the fundamental societal choices we hold: the social market economy, health protection, food security, fair and efficient financial regulation … it is up to the British to tell us whether they still adhere to the European model.

“Their answer is important because it directs the discussion on our future partnership and the conditions of its ratification.”

During his visit to the UK earlier this week, Ross said he was hopeful an initial scoping exercise on a UK-US trade deal could bear fruit, but that he would want to see the British government drop regulations that he believed did not have scientific foundation, such as the ban on US chlorinated chicken. Ross had also described the EU as protectionist.

Speaking as the EU and British Brexit negotiating teams resumed talks in Brussels without their principal negotiators, Barnier said the EU would not allow Britain to undercut the bloc’s regulatory standard in place. “There will be no close commercial relationship without a level playing field’, he said.

He also emphasised that it was high time for the UK to provide clarity on how much of its estimated €60bn (£53bn) divorce bill it is willing to pay.

Germany is leading EU27 states in pressuring their negotiating team to take a stricter line in Brexit talks, offering the British government no hope of discussions on a future relationship with the bloc unless a definitive concession on the financial settlement is made in the next few weeks.

At a meeting of ambassadors on Wednesday evening, the EU27 states told Barnier of their “disappointment and surprise” at the UK government’s failure to offer any further details on the budget commitments it was willing to honour on the leaving the EU.

One senior EU diplomat said Barnier was “under a bit of pressure” by the member states to ensure discussions do not develop beyond the unpicking of the opening withdrawal issues.

“The member states want to be careful. We are not going to swim into the UK’s net,” one source said, on condition of anonymity.

London insists there should be at least some talks on future arrangements at this stage in order help settle the opening withdrawal issues of the financial settlement, citizens’ rights and the border between Northern Ireland and the Republic.

The UK is making a fresh push for bilateral talks with member states on the future right of UK nationals to vote in their adopted home nations in municipal and European elections.

It is within the power of each of the member states to decide on its policy, but the European commission is blocking bilateral discussions on the subject, UK government sources said.

Jacqueline Foster, the deputy leader of Conservative MEPs, said: “The UK set out a fair and reasonable offer on citizens’ rights which is nearly ready to be signed. One of the remaining issues is the right to vote and stand in elections, but there seems to be a catch-22.

“The commission say it’s for the member states to sort out, but tell the member states they shouldn’t talk to the Brits”.

The commission denies that it is blocking the British from discussing voting rights with the member states, while insisting it remains in its power to do so.

The latest round of talks kicked off as the European commission said the UK would have almost the slowest economic growth of any EU country when it leaves the bloc in 2019.

According to the commission’s autumn forecast, the British economy will grow 1.1% in 2019, only slightly ahead of Italy, and far behind the 1.9% expansion across the eurozone.

The forecast is based on the theoretical assumption the EU and UK will maintain the status quo after Brexit day, but takes into account business uncertainty that is choking off investment.