Business groups from across northern Europe have urged both sides in the Brexit talks to agree a trade deal as soon as possible - with the UK staying in the single market and customs union during a transition period.
The call from chambers of commerce from seven countries said firms need to start preparing for any new arrangements but most of the "big issues" of concern to businesses had "not yet even been touched on" by UK and European Union negotiators.
They demanded clarity on the outlines of a future EU-UK trade agreement over the coming months and warned they were "increasingly concerned about continued rhetoric on a no-deal scenario".
The joint call comes from the British Chambers of Commerce (BCC) and counterpart organisations in Ireland, Germany, France, the Netherlands, Denmark and Belgium - countries that account for around 70% of EU-UK trade.
In a message to Brexit Secretary David Davis and EU negotiator Michel Barnier, they urged both sides to "create clarity on the outlines of a future trade friendly EU-UK relationship in the following months".
They added: "Given the monumental changes Brexit will bring, a realistic transition period is needed to provide time for companies to adapt to the new EU-UK trading relationship.
"A status quo-like transition period - announced with sufficient notice - ensuring the UK remains in the customs union and the single market for the duration of the transition period, with all the appropriate rights and obligations, would be best to provide business with the highest possible degree of certainty and predictability."
Theresa May has repeatedly stressed that "no deal is better than a bad deal" and some hardline Eurosceptics have urged the Prime Minister to walk away from talks and leave the bloc on World Trade Organisation terms.
But the chambers of commerce warned: "A 'no deal' scenario would be extremely undesirable for business as this would mean they will be faced with higher tariffs, more burdensome customs procedures and longer delays than under a negotiated separation."
BCC director general Adam Marshall said the breakthrough in the negotiations, with Brussels indicating that "sufficient progress" had been made on divorce issues to move on to trade talks, was a relief to business.
Calling for trade talks to start without delay, he said: "There is a real clamour for the negotiations to start on the practical issues that will affect firms, from regulation and customs, to tariffs and taxes.
"Businesses trading between UK and Europe have done their best to focus on the potential impact of Brexit on their operations, rather than on the day-to-day political noise.
"However, businesses both in the UK and around the world want clarity on the key political issues, and it is up to the negotiators to provide that clarity."