British diplomats will pull out from the EU’s institutional structures of power in Brussels within days, under plans being drawn up by Downing Street.

In an attempt to reinforce the message that the UK is leaving the EU by 31 October, “do or die”, the UK will stop attending the day-to-day meetings that inform the bloc’s decision-making.

The move under discussion is said by UK officials to be in line with Boris Johnson’s first statement in the House of Commons, in which he said he would “unshackle” British diplomacy from EU affairs.

Critics have countered that the symbolic walkout would merely leave the UK blindsided on decisions and ultimately damage the national interest.

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EU working group meetings at which British diplomats were expected to take their seats alongside the other 27 member states will deal with issues on security, the pan-European response to any future crises involving civilians, foreign affairs and the protection of consumers interests.

It is unclear how far the UK’s withdrawal from the EU structures would go before 31 October, and whether ministers or the UK’s permanent representative in the EU would ultimately fail to show up for meetings in September and October.

The foreign secretary, Dominic Raab, said he would attend a meeting of his EU counterparts at the end of August in Helsinki.

Luisa Porritt MEP, the deputy leader of the Liberal Democrats in the European parliament, said: “Boris Johnson is unnecessarily sabotaging British influence in Europe.

“Haughty grandstanding like this undermines our place in the world and will be treated as a snub by our European neighbours and allies, who we should be working with to address shared challenges.

“Margaret Thatcher and Winston Churchill would be appalled by this short-sightedness. We should be leading in Europe, not undermining our own interests.

“To be outside the room while our shared security interests are being discussed shows weakness and pettiness, not strength. Brexit is not inevitable; this national humiliation must end alongside this rotten Conservative government.”

There are about 150 diplomats in the UK’s permanent representation in Brussels lobbying for British interests during the drafting of EU positions and regulations.

Far from being keen to abandon the field in Brussels, Theresa May’s government had been looking at how to maintain ways into the EU’s institutions in order to influence events from outside.

But in his statement to the Commons on becoming prime minister, Johnson had said that both sides needed to recognise the “reality” that the UK’s “national participation in the European union” was coming to an end.

The prime minister claimed there were “very many brilliant officials trapped in meeting after meeting in Brussels and Luxembourg when they could be better deploying their talents in preparing to pioneer new trade deals and promoting a truly global Britain”.

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While the UK has not played its usual full role in meetings in areas on the future of the EU, including in discussions on the bloc’s budget, it has been an active player in other fields such as foreign affairs since the Brexit referendum in 2016.

EU diplomats said they would regret any decision by the British government to prematurely leave the Brussels institutions where the UK diplomats have built up a strong reputation.

“They were once the most respected diplomatic corps here,” one said. “That was diminished during David Cameron’s government but the UK representative’s position was always important. Even in areas where the UK did not have a strong national stance, they would have ideas to solve a problem.”

Paul Adamson, a visiting professor at the Policy Institute, King’s College London, said the UK government would need to build up its embassy in Brussels after Brexit.

He said: “One of the many ironies of Brexit is that the UK government will have to significantly increase its diplomatic presence in Brussels - as well as in key EU capitals - both to find out what is going on in meetings from which it will be excluded but also to try to influence the direction of EU policy making. Brussels decisions will continue to impact the UK.

“[The government] and its agencies will have to invest heavily in public diplomacy to repair alliances and to forge new ones. The private sector, whether its business, civil society, the think-tank world and the like, will very much need to be part of this exercise”.

A government spokesman said: “We are leaving the EU whatever the circumstances on 31 October. It therefore makes sense to review our attendance at EU meetings to make sure we are making the best use of government time. This process is ongoing.”