The two sides are due to hold a third round of negotiations next week but the officials were unable to say if they would start on Monday, as widely expected, or Tuesday.
The EU insists there has to be "sufficient progress" in three key areas -- EU citizen rights, Northern Ireland's border and the exit bill -- before considering London's demand for talks on its future trade relationship with the bloc.
"It is not the lack of time that is preventing us from advancing, so far it has been the lack of substance," added the official who asked not to be named.
The EU officials stressed repeatedly that the remaining 27 member states had agreed on the sequencing of the talks and despite London pressing to get the future relationship on the table, that was a no-go for the moment.
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London has published several position papers in the past few weeks but the EU officials appeared not to be overly impressed.
On the future of Northern Ireland and its border with the Republic of Ireland, London suggested technological solutions could avoid it becoming a barrier to both trade and the peace process.
"We see a lot of magical thinking about how an invisible border could work in the future," one of the officials said, urging London to really take on board just how big an impact Brexit will have on Ireland's economy and society.
In another position paper, Britain said there might be room for the European Court of Justice to have an indirect influence, apparently softening its position that the EU's top court would have any future say at all.
But again this would not be good enough, the official said.
The rights of more than three million EU citizens in Britain and one million Britons in Europe arose from EU law and therefore come under the remit of the ECJ, they said.
As for Britain's divorce settlement -- estimated at up to 100 billion euros in Brussels but much less at 40 billion according to reports in London -- the officials said it was not a numbers game but one of agreeing how to work out the bill.
"We have to have a methodology sufficiently detailed so that commitments made to various beneficiaries of the EU budget will be honoured," one official said.
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