EU officials fear they are being "bugged" by the British secret service after the UK obtained sensitive documents within hours of them being presented at a meeting, according to a report.
The fears were raised at a European Council meeting on July 13 by Sabine Weyand, the deputy of chief Brexit negotiator Michel Barnier, a "highly placed" EU source told the Telegraph.
She reportedly told officials attending the meeting of the European Council's Article 50 Working Party that "it could not be excluded" that British intelligence had infiltrated their meetings.
Their fears were prompted after British negotiators obtained the contents of a "politically explosive" slide presentation almost immediately after they were shared among EU officials on July 5, one day before May assembled her Cabinet for crunch talks at Chequers, the report said.
The slides are said to contain "highly negative" economic assessments of British plans to remain in the EU's single market for goods.
The UK had within hours lobbied at the "highest level" to block the European Commission from publishing the slides, which would have been interpreted as a pre-emptive strike against May's Chequers proposals, the source told the Telegraph.
The slides have not been published but are said to raise serious questions about the viability of Theresa May's Brexit blueprint, which proposes that the UK remain within the single market for physical goods but diverges in other areas.
The news comes as British negotiators head to Brussels on Thursday to resume two days of technical Brexit talks, although little progress is expected to be made on substantive issues .
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