The EU has slapped down the UK Government after it attempted to bypass Brussels on post-Brexit trade rules.

Documents obtained by The Independent show the European Commission was unhappy after British officials asked each member state directly about their plans to cope with new checks on goods coming into the UK.

At one point, the EU Commission told countries in the bloc to ignore the UK government completely. It then sent a memo telling member states to provide only “short general information” because of the “problematic” nature of the British request.

The Commission later warned the UK that contacting each country directly was “outside” the terms of Boris Johnson’s Brexit trade deal – saying it was of “significant concern” since a proper response to British queries should be “harmonised at EU level”.

The rebuke emerged as Rishi Sunak’s government comes under pressure from both the EU and British business bosses to spell out exactly how the latest controls on imports, due to come into force in October, will work.

Peter Mandelson, the former business secretary and EU trade commissioner, said trying to circumnavigate Brussels was always going to backfire.

He told The Independent: “It is tempting to try and go round the Commission, but this doesn’t work and is counterproductive.

“The British government should be doubling down on a good relationship with the Commission and building trust. Britain desperately needs this in order to mitigate our losses in trade.”

Trade experts also said it had been “unwise” to try to go round Brussels chiefs and was indicative of a “still-struggling relationship” ahead of another mountain of red tape for firms across the continent to navigate.

One food industry expert said the memos showed “unhelpful friction” between the UK and the EU at a time when they should be working together to avoid major disruption later this year.

The issue began when officials from the UK’s Department for Environment, Food and Rural Affairs sent a message to EU member states on 2 June, asking each to fill out a questionnaire on their readiness to deal with new controls on food and agriculture trade.

A June 9 memo from the European Commission, forwarded to member state diplomats by Council of the EU officials and passed to The Independent, warns: “Member States are advised not to respond to the online questionnaire requested by the UK”.

On the same date, an official at DG SANTE, the Commission’s health directorate, wrote to officials at Defra warning against “the use of channels outside” the EU-UK trade agreement for such matters.

A follow-up, sent to member states from the Commission on 21 June, says member states “wishing to respond” should avoid giving too much detail.

After telling members states it was “harmonising” communication with the UK, the EU Commission then shared its own list of more than 70 questions for London – grilling British officials on preparations for the 31 October import controls.

The Independent understands the UK government explained to Brussels that it was willing to work through the EU Commission.

But David Henig, a director at the European Centre for International Political Economy (ECIPE), said UK officials should have known that Brussels coordinates responses to avoid any potential divisions on Brexit issues.

The Brexit expert said “it looks unwise for the UK to have approached the issue in this way, something that could damage the trust we need”. Mr Henig said the row was “symbolic of a still-struggling relationship – it’s more friction that we don’t need”.

Dr Kirsty Hughes, director of the Scottish Centre on European Relations (SCER), said the memos appeared to show the EU “implicitly advising member states that if they give the unintentional impression they are fully ready, then the UK might use that to blame them if there is disruption”.

David Davis, the UK’s first Brexit secretary who led talks with the EU from 2016 to 2018, told The Independent it would not be the last time this happens.

“This is going to happen time and time again in the coming years. Good diplomacy tries to understand the person you are negotiating with or deal with, always.

“So you’re always going to rub into this and the Commission for its part, perfectly properly, is always going to try and maintain a common front.

“That’s what comes out of these things: it certainly isn’t the first time and it certainly won’t be the last time it happens, I’m sure.”

Sir Malcolm Rifkind said the EU is “probably correct” but that the Commission “should not be so bureaucratic about it”.

“Trade is an EU responsibility not the responsibility of individual member states, so to be strictly correct the proper communication should be with the EU people responsible for trade,” he said. “They could have treated it a bit more lightly. It is not exactly a capital offence.”

Britain’s food and logistics leaders have also warned that the coming wave of post-Brexit red tape could cause disruption and worsen the inflation crisis by pushing up food prices at the supermarket.

Shane Brennan, chief executive of the Cold Chain Federation, warned there was still a “lot of uncertainty and confusion” among European businesses about what certificates they need and how border controls will operate. “They’re not confident it will go smoothly.”

He said the “unhelpful friction” came at a time that UK firms and port chiefs were “livid” they did not have enough information from the government on how the import checks are supposed to work.

“There’s going to be a period of disruption and paralysis,” he told The Independent. “There’s still so many unanswered questions – yet again we’re going to have to deal with it when it comes. It’s a complete mess.”

Mr Brennan said it still wasn’t clear exactly which kinds of food and agricultural goods would fall into low, medium and high-risk categories demanding different kinds of controls, although outlines from Defra have been given as part of the “target operating model”.

He also said it wasn’t yet clear which digital forms had to be uploaded to the UK government website from 31 October – given that it the autumn is supposed to represent a “soft launch” and some physical inspections won’t begin until January.

An EU official said: “It is up to the UK to draw up a workable import regime, taking into account the significant volume of exports from the EU to the UK.

“Nevertheless, the Commission is in close contact with the UK authorities and member states in order to understand the consequences and requirements resulting from the future implementation of the ‘Border Target Operating Model’ for the EU.”

A government spokesperson said the target operating model “will transform the UK’s border controls” and create “a new world-class system to provide protection from security and biosecurity threats”.

They said the system would prevent delays at the border “through a reduction in the need for physical checks and by ensuring that checks take place away from ports where this is needed to allow traffic to flow freely”.

The spokesperson added: “We continue to engage extensively with industry and will publish the target operating model shortly.”