BRUSSELS (Reuters) - European leaders welcomed on Thursday that Boris Johnson's expected election victory provided clarity on Britain's withdrawal from the EU, but said it would be challenging to agree a post-Brexit trade deal by the end of 2020.
Exit polls showed Johnson's Conservative Party would enjoy a majority of 86 seats in the 650-seat British parliament.
"It is a very clear result - it will not change by tomorrow morning," Swedish Prime Minister Stefan Lofven told reporters in Brussels after the first day of an EU summit.
"It means that we will move forward with our separation now. We now have 11 months to hash out a deal (on the future trade agreement). It's a very short time," he said.
EU leaders will discuss on Friday a mandate for the European Commission to negotiate the future relationship with Britain after Brexit now expected at the end of January, with a transition period until the end of 2020.
"The most important thing with Brexit is not the way we divorce, it's what we build afterwards," France's European affairs minister Amelie de Montchalin told reporters.
Britain and the EU have to negotiate a trade deal by the end of 2020 because that is when a transition period for Britain's withdrawal ends. Without a new deal, trade relations between London and its biggest trading partner - the EU - could be based on basic to World Trade Organization terms.
"We are ready to negotiate whatever is necessary, and it will be important tomorrow to get the mandate for the steps from the council (of EU leaders)," European Commission President Ursula von der Leyen said.
But EU officials warn that negotiating a trade deal with Britain in less than 12 months will be very difficult. EU trade agreements normally take years to be negotiated and enter force.
"(It is) a tall order to move on the future relationship in such a short time," one EU official said.