German industrialists have warned that British hopes of their support in Brexit negotiations are misplaced and could backfire with dangerous consequences for international trade. Business leaders in Europe’s biggest economy are instead calling on Conservatives to rethink their commitment to leaving the single market, even though the party has doubled down on this promise in its election manifesto. David Davis and Boris Johnson have repeatedly cited likely pressure from German exporters, such as carmakers, as a reason for thinking they can persuade European negotiators to maintain free trade access after Britain leaves. But the theory is increasingly rejected by those whose support they need most – scepticism relayed most forcefully by Steffen Kampeter, the chief executive of the German employers’ federation, on a trip to the UK this week. “The top priority of European business is the integrity of the single market; the second priority is making good business with the UK. We will see if there is a conflict, but the message is: do not harm the single market by cherry-picking deals,” he told a conference of British business leaders in London this week. “It’s not the German carmakers that are directing the negotiations,” added Kampeter, who said he knew of no one who thought a trade deal within 18 months was possible and called for “rhetorical disarmament on all sides”.