Germany has claimed the UK owes its privileged status as an economic powerhouse and position within the G7 to its membership of the European single market.
In a speech to the Federation of German Industries (BDI), Martin Schulz, leader of Germany’s Social Democrats (SPD), said neither side in the Brexit negotiations had fully understood the dramatic implications of the UK turning its back on the bloc.
Describing it as “a veto power, a nuclear power, a G7 member, the second-largest economy in the single market”, Mr Schulz warned the UK it would “pay a steep price” for turning its back on the EU
Mr Schulz, a former European Parliament president, said: “The British have to ask themselves: Why are they still part of the G7? Why are they still the second-largest economy in the single market?
“Precisely because they have unrestricted access to this single market.
“This access is what the British have decided to cut off.”
Without mincing his words, the centre-left candidate for German Chancellor, condemned Brexit, describing it as as “the result of a shameful campaign by unscrupulous populists relying on fake news, who are selling out an entire generation”.
He added Brexit would make it harder for the EU to deal with the most pressing challenges of the hour, including security, climate change, migration and the fight against terrorism.
The German, added: "The best result of the Brexit negotiations would be - there wouldn't be a Brexit."
Mr Schulz comments come just hours after Chancellor Angela Merkel urged the remaining 27 members of the EU to stick together during Brexit talks, which began on Monday, adding the talks were important for the future of European integration.
Speaking in reference to the remaining EU 27 and the 19 eurozone countries, Mrs Merkel, said: "The risk of the exit negotiations with Britain is that we do not take adequate care of our own future.
Let's stay together, let's not divide from each other.”
The German Chancellor added she wanted the talks to be conducted "in a good spirit" and Britain's position would become evident in the coming months.
She said: "We will of course implement what Britain pitches, but in a way that the interests of the 27 member states are safeguarded."
At their first meeting in Brussels on Monday, British and EU negotiators agreed on a timetable for the Brexit talks, with both sides stressing their goodwill but acknowledging the task's incredible complexity and increasingly tight deadline