The EU’s chief negotiator’s office has poured cold water on Theresa May’s latest plan for a Brexit trade deal, warning that her suggestion of mutual recognition of standards is not enough to secure access to the single market.

Stefaan de Rynck, the main advisor to chief negotiator Michel Barnier, said the EU’s current approach to trade necessitated a “single EU rule book” – which would appear at odds with the PM’s latest idea.

In her Mansion House speech last week, Ms May suggested that the EU and UK could negotiate a trade deal where they mutually recognised each others’ rules and standards as obtaining the same “regulatory outcomes”, with a third-party independent court overseeing disputes.

Are referendums a good thing?

But Mr De Rynck said in a lecture at LSE on Monday: “The EU has moved away in the wake of the financial crisis from mutual recognition of national standards to a centralised approach with a single EU rule book and common enforcement structures and single supervisory structures.

“If you are in a very integrated market but you don’t have the joint enforcement structures then you can see the potential for all kinds of difficulties.”

The EU’s chief advisor said the ECJ would be able to declare the mutual recognition of standards invalid if it undermined single market integrity, and that this was fundamental to the idea of what the single market was.

What could the sticking points be in the Brexit trade deal?

His comments are the most detailed response from the European Commission to the PM’s latest speech yet. Chief negotiator Michel Barnier gave a fairly muted reaction last week, saying he welcomed the address and that it would be taken into account when drawing up the EU’s draft trade guidelines, which are expected to be released on Wednesday.

The biggest issues facing UK on leaving EU Show all 8 1 /8 The biggest issues facing UK on leaving EU The biggest issues facing UK on leaving EU Post-Brexit immigration workers sorting radishes on a production line at a farm in Norfolk. One possible post-Brexit immigration scheme could struggle to channel workers towards less attractive roles - while another may heighten the risk of labour exploitation, a new report warns. PA The biggest issues facing UK on leaving EU Customs union A key point in the negotiations remains Britain's access to, or withdrawal from, the EU customs union. Since the referendum there has been hot debate over the meaning of Brexit: would it entail a full withdrawal from the existing agreement, known as hard Brexit, or the soft version in which we would remain part of a common customs area for most goods, as Turkey does? No 10 has so far insisted that “Brexit means Brexit” and that Britain will be leaving the customs union, but may be inclined to change its position once the potential risks to the UK’s economic outlook become clearer. Alamy The biggest issues facing UK on leaving EU Northern Ireland-Irish border Though progress was made last year, there has still been no solid agreement on whether there should be a hard border between Northern Ireland and the Republic of Ireland. To ensure borderless travel on the island, the countries must be in regulatory alignment and therefore adhere to the same rules as the customs union. In December, the Conservative Party’s coalition partners, the DUP, refused a draft agreement that would place the UK/EU border in the Irish Sea due to its potential to undermine the union. May has promised that would not be the case and has suggested that a “specific solution” would need to be found. Getty The biggest issues facing UK on leaving EU Transition period Despite protests from a small number of Conservative MPs, the Government and the EU are largely in agreement that a transitional period is needed after Brexit. The talks, however, have reached an impasse. Though May has agreed that the UK will continue to contribute to the EU budget until 2021, the PM wants to be able to select which laws made during this time the UK will have to adhere to. Chief negotiator Michel Barnier has said the UK must adopt all of the laws passed during the transition, without any input from British ministers or MEPs. EPA The biggest issues facing UK on leaving EU Rights of EU citizens living the UK The Prime Minister has promised EU citizens already living in the UK the right to live and work here after Brexit, but the rights of those who arrive after Brexit day remains unclear. May insists that those who arrive during the transition period should not be allowed to stay, whereas the EU believe the cut-off point should be later. Getty The biggest issues facing UK on leaving EU Future trade agreement (with the EU) Despite this being a key issue in negotiations, the Government has yet to lay out exactly what it wants from a trade deal with the EU. Infighting within the Cabinet has prevented a solid position from being reached, with some MPs content that "no deal is better than a bad deal" while others rally behind single market access. The EU has already confirmed that access to the single market would be impossible without the UK remaining in the customs union. Getty The biggest issues facing UK on leaving EU Future trade agreements (internationally) The Government has already begun trying to woo foreign leaders into prospective trade agreements, with various high profile state visits to China, India and Canada for May, and the now infamous invitation to US President Donald Trump to visit London. However the UK cannot make trade agreements with another country while it is still a member of the EU, and the potential loss of trade with the world's major powers is a source of anxiety for the PM. The EU has said the UK cannot secure trade deals during the transition period. EPA The biggest issues facing UK on leaving EU Financial services Banks in the UK will be hit hard regardless of the Brexit outcome. The EU has refused to give British banks passporting rights to trade within the EU, dashing hopes of a special City deal. However according to new reports Germany has suggested allowing trade on the condition that the UK continues paying into the EU budget even after the transition period. Getty

Others in Brussels, however, gave a more frosty suggestion, with European Parliament chief negotiator Guy Verhofstadt saying the PM needed to move beyond “vague aspirations”.