German car chief Matthias Wissmann warns over Brexit
The government has been urged to clarify its policy on leaving the European Union by the head of the German automobile industry association.
Matthias Wissmann warned that prolonged uncertainty could damage investment in the UK, where German manufacturers have about 100 production sites.
Mr Wissmann told the BBC that the UK leaving the single market could force companies to move business elsewhere.
Germany also exports more vehicles to the UK than any other country.
Mr Wissmann, president of the German Automotive Association, said: "We need, relatively soon, a clear answer... Will we have tariff and non-tariff barriers between Britain on the one hand and the European Union?
"That means a long period of uncertainties will block future investments in Britain, and that makes me really concerned.
"Therefore I hope that the British government, at a certain crossroads within the next 12 months, decides to go for the single market and not for any other regime which would need years to discuss and negotiate.
"Five or 10 years of uncertainties would be not very positive for both sides, the European Union and Britain."
On Tuesday, Brexit Secretary David Davis described his meeting with the European Parliament's chief negotiator Guy Verhofstadt as a "good start".
Although they could not negotiate yet, he said their discussions had been able to cover structures and how both sides propose to approach the Brexit talks.
He said a deal was possible that was in the interests of the EU and the UK.
Mr Verhofstadt said he wanted an exit deal completed before the next European Parliament elections in 2019.
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