A group of influential German business figures have launched a campaign to keep the UK in the European Union.
The alliance, dubbed a New Deal for Britain, includes three ex-presidents of the Federation of German Industry.
One of the three, Heinrich Weiss, said: "With Britain, the EU is losing its most important ally in the fight for competitiveness."
They will lobby European governments to offer more concessions to the UK, in particular on immigration.
'Battle for Britain'
The Federation of German Industry (BDI) is the German equivalent of UK business lobby group the CBI.
The other leading ex-BDI figures are Michael Rogowski and Hans-Olaf Henkel, who is now an MEP.
"We want to launch a Battle for Britain with this initiative, we need a new offer from the EU, this call is addressed to Brussels and also to Berlin," said Mr Henkel.
The message may not go down too well in Berlin, where the official - and prevailing - position is that EU integrity matters more than a good deal for the UK.
But the breakaway group of influential economists and industrialists is demanding European governments take a more compromising stance.
The alliance - which fears Brexit will trigger economic turmoil in Europe - will also call on the UK government to change its mind about leaving the EU.
The Eyes On Events's Berlin correspondent, Jenny Hill, said: "In reality the group is unlikely to significantly alter Germany's position.
"But these are influential voices and their message does echo a more widespread concern in Berlin at the current state of Brexit negotiations."
It comes as the EU says it is ready to offer the UK the "most ambitious" free trade deal if it meets its conditions on Brexit.
The EU's chief negotiator, Michel Barnier, said: "If we manage to negotiate an orderly withdrawal and establish a level playing field... the EU will be ready to offer its most ambitious FTA [free trade agreement] approach."