Dieter Kempf, the head of the German Industry Federation (BDI), made his comments as the third round of talks between Brexit negotiators begin this Monday in Brussels.
Mr Kempf warned: “But with such bad conditions, hardly any progress can be expected.”
According to schedule, Brexit will be completed in March 2019.
Ultimately the objective is an agreement to make the consequences of the British departure as smooth as possible for millions of affected citizens and the economy.
The British Government had published a number of position papers in recent weeks – but they have met with little agreement with the EU.
BDI chief Kempf also criticizes the British ideas submitted a few days ago for a future customs agreement, saying they are associated with “disproportionately high bureaucratic efforts”.
He went on: “These ideas are far away from business practice. The United Kingdom must finally make clear statements about the exit modalities.”
The Brexit Commissioner of the European Parliament, Guy Verhofstadt, also called on the government in London to present concrete proposals on the core elements of a Brexit agreement.
“We will only be able to talk about our future relationship if we have made appreciable progress in the three most important areas,” said the former Belgian head of government of the “world”. These included the rights of EU citizens, British financial commitments and the future regulation of the Northern Ireland – Republic of Ireland border.
The British Government, on the other hand, is urging the EU be more flexible.
London wants to negotiate on issues of separation from the EU and on the future relations of both sides at the same time.
The EU Commission, on the other hand, wants to impose its demands on the United Kingdom, including British payments of up to 100 billion euros for projects it had signed up to before the referendum last year.