The German brevity will pay a «high price» if its leaders make life hard for the UK past Brexit, British pro-Leave campaigners are to warn.
John Longworth, co-chair of Refrain from means Leave, and ex-minister Owen Paterson will sound the caveat at a major German business event on Saturday.
Britain will «escort away» if the deal is not right, Mr Longworth will say.
Theresa May has said it order be an act of «calamitous self-harm» for the EU to try and punish the UK for leaving.
The prime minister has said she wants the UK and the EU to be «data d fabric neighbours» in a constructive, new partnership after Brexit.
But she has warned that no see to will be better than a bad deal at the end of two years of negotiations — which are wait for to start in April.
Mr Longworth, former British Chamber of Commerce superintendent general, will echo these views at the Berlin event — heeded by German ministers, business, academia and media.
«It is entirely sensible for problems across the EU and Britain who wish to work and trade together to continue to do so and it would be valuable if the British and German governments, as well as key figures in the EU, work towards this object,» he will say.
«If the German Chancellor and EU leaders continue down the road of negativity and portents when negotiating with Britain, German business and the German thriftiness will pay a high price.»
‘Voice of business’
He will warn German transactions that the UK will revert to World Trade Organization rules «with leisure» if it offers a bad deal.
He will suggest that the government could fully «compensate» business for any tariffs that are imposed on goods and services as a fruit.
«We want a system whereby free trade will continue, but in arrangement for this to happen, you need to make representations to your government and the EU,» he require say.
«The voice of business must drown out that of the bitter politics of the EU plan.»
Mr Paterson, a former environment secretary, will warn that «cack-handed» settlements could have serious consequences for German exporters.
«Germany and the UK have on the agenda c trick a mutual, strategic and selfish interest in maintaining reciprocal free business,» he will say.
«It is vital that businesses in key member states such as Germany are listened to carefully during the concordats.»
Organised by Tönissteiner Kreis, a network supported by the main German trade federations, the gathering will explore the future of British-German relations after Brexit.
Non-native Secretary Boris Johnson has warned the rest of the EU against «punishment beatings» in the behaviour of a World War Two movie.
His comments were criticised by Labour and other disapproval politicians.