European Commission Vice President Maros Sefcovic said the decision was “very important politically” and that it meant Brexit Britain “would treat the European Union delegation in worse terms than any other country on the planet.”
Mr Sefcovic told the Financial Times: “I’m sure that it’s very important for the UK that their diplomats here are properly treated and have appropriate access, and it’s very important for us to have the same in London.”
Mr Sefcovic has been tasked to oversee the future trading relationship between the UK and the Brussels bloc.
He warned the bloc’s foreign ministers have raised concerns over the matter at a recent meeting.
“We do not want to exaggerate or dramatise the situation but we clearly want our British colleagues and partners to know that this is an issue, which we hope we will solve through the discussions,” he said.
“The UK knows pretty well that we are not just an international organisation,” he added.
Britain’s decision was also lambasted at home when House of Lords peers described the move as “vindictive” and “offensive” on Tuesday.
Foreign Office minister Lord Ahmad of Wimbledon said the Government continued to engage with the EU on the long-term arrangements for the EU delegation.
Lord Ahmad told peers that he did not wish to pre-empt those talks and insisted the Government wanted a relationship based on “friendly cooperation” with the EU.
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Lord Ahmad said the Government continued to negotiate and work with the EU on the long term arrangements and wanted an “optimum outcome” which worked for both sides.
Tory Baroness Hooper said the decision was “gratuitously offensive” not only to Brussels and the EU states but also to Portugal as the ambassador was a Portuguese diplomat.
She asked what benefit this “unnecessary action” could bring for Britain.
Lord Ahmad said he could not pre-empt discussions with the EU but assured peers that the EU delegation would have all the privileges and immunities they needed to “function effectively”.
It emerged last week that ambassador Joao Vale de Almeida had not been given the same status as ambassadors sent by national governments.
Mr de Almeida is the EU’s first ambassador in London after the UK’s departure from the bloc.
In the Lords, Liberal Democrat Baroness Ludford suggested the Government was “squandering goodwill” and acting in a “petty” fashion.
Lord Ahmad said the Government wanted the UK to be the “best ally and the best partner to the EU”.
Tory former Cabinet minister Lord King of Bridgwater urged ministers to sort the issue out as quickly as possible “so we live up to intention of being the best friend and ally” of the EU.
Former diplomat Lord Jay of Ewelme said it was time to put aside “gesture politics” and focus on developing relations necessary to make a success of the G7 summit.
Labour’s Lord Liddle questioned even the need for discussions on the ambassador’s status and accused the Foreign Secretary of searching for “cheap points” that will go down well with Brexiteer backbenchers.
Lord Ahmad denied this, insisting Dominic Raab had close working partnerships and friendships across the EU.