The German chancellor was grilled by reporters over what the vaguely defined term, as laid down in the bloc’s negotiating guidelines, specifically entails after leaders took just 90 seconds to decide not to open trade talks with Britain.
But despite the fact that European capitals are asking the UK to achieve this threshold, Mrs Merkel appeared to have no idea what it actually meant and fobbed off responsibility for its definition onto Mr Barnier.
However, as the bloc has repeatedly made clear it is the exclusive competence of the EU27 leaders – and not the Frenchman – to determine whether sufficient progress has been made in the talks.
The farcical moment came as Mrs Merkel debriefed media in Brussels following this week’s EU Council summit, at which Mrs May made a personal plea to fellow member states to move the divorce talks forward.
She said: “As regards the clear definition of sufficient progress I won’t be able to give you any details because that is left to the negotiations between the British and Michel Barnier.
“As far as substance is concerned everybody knows what needs to be done, what has to happen now. Sufficient progress was a sufficiently carefully chosen term or language. We’ve been clear and we want to stand by that.”
The bloc’s official negotiating guidelines state: “The European Council will monitor progress closely and determine when sufficient progress has been achieved to allow negotiations to proceed to the next phase.”
The European Council is made up of the leaders of the 27 member states whereas negotiator Mr Barnier, who was approved by the member states and MEPs, is employed by Jean-Claude Juncker’s EU Commission.
Mrs Merkel’s candid remarks will open up the EU to accusations that its talks strategy is not as watertight as it seems and is also likely to raise questions about how Britain can reasonably be expected to meet a target its negotiating partner cannot even define.
Elsewhere the Berlin chief also made no secret about the fact that money is now at the forefront of European minds, answering a question about what Britain can do to break the deadlock by making an exclusive reference to the Brexit bill.
The Chancellor said the UK prime minister had held a number of bilateral meetings with European leaders in the run up to today’s summit, all of whom had stressed to her the importance of upping her cash offer.
And she also described Mrs May’s proposal for a two-year transition period on current membership terms as an “interesting idea” but said it cannot be agreed by the EU until the Brexit bill is settled.
She said: “We’ve been quite clear on why we think sufficient progress hasn’t been made in relation to the financial commitments therefore it’s quite clear what needs to be furnished further.
“Michel Barnier provided us with an overview of where the negotiations are right now, no sufficient progress has been noted to begin with stage two here and now we focussed very much on wanting to carefully prepare that second phase on behalf of the EU27.
“We’ll have to identify the various conditions for Brexit. Much work remains to be done here on the part of the EU27. We’re coordinating our efforts very closely, the links that have been established over the years are very close so it will require a lot of work.
“We’d hope that we will be ready by December to initiate phase two but this depends to a large extent on the extent to which Great Britain prepares progress to such an extent that we can call it sufficient. The topic of financial commitments is of course the dominating issue in that regard.”