Martin Selmayr, chief of staff to EU Commission president Jean Claude-Junker, gave a bleak assessment of Britain's prospects during talks to withdraw from the bloc.
And he revelled in his reputation as the "monster" of Brussels, describing his nickname as "flattering".
Describing the current Number 10 administration, Mr Selmayr told the Financial Times: "In London it's like a bunker, it was a bunker in Cameron's time and it is a bunker now – it's even worse.
"It's difficult to communicate and understand each other if you don't come out of the closet."
A key EU official has said Theresa May's government is 'worse' than Cameron's for communicating
Mrs May and Brexit minister David Davis have kept their cards resolutely close to their chests in the run up to Brexit talks startiing.
They were successful in defeating amendments to the PM's Brexit bill seeking guarantees over EU citizens living in Britain, arguing Number 10 did not want to "show its hand" before Brussels did.
But Remainers, including Lib Dem leader Tim Farron, have claimed the stance is less to do with keeping a poker face and more likely the Government has no firm plans on how to approach the negotiations.
One of the biggest hurdles facing negotiators is the controversial £50billion 'Brexit Bill" – a demand Mr Selmayr is reportedly pushing for personally.
Martin Selmayr has been described as the 'monster of Brussels'
Selmayr is seen as President Juncker's pitbull
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In London it's like a bunker, it was a bunker in Cameron's time and it is a bunker now – it's even worse
He was also critical of the way British ministers conducted themselves in Europe.
"It's very hard to judge how they see things," Mr Selmayr said of Whitehall staff, adding they were "never here [Brussels] to talk to us".
Mr Selmayr said he first saw the fundemental difference between Britain and the rest of Europe during a speech by Margaret Thatcher in 1993.
He said the former Prime Minister 'blasted" her successor John Major for his pro-Europe stance and said: "For the Germans and French it is unthinkable to see the European project only as a market.
"It is an instrument to achieve something more."
Mr Selmayr has a fearsome reputation with the EU as an enforcer, stamping his and President Junker's authority on all Commission policy.
He been dubbed a "monster" and a "Rasputin" type figure for his authoritian style – and seems happy with the labels.
He said: "It can be flattering if it means I'm not a wimp."