LONDON/BRUSSELS (Reuters) - Britain and the European Union struck a pessimistic tone in trade talks on Thursday, with a spokesman for Prime Minister Boris Johnson saying it was “very likely” there would be no agreement unless the bloc changed its position “substantially”. ADVERTISEMENT: Your content will begin in 23 seconds Just over two weeks before Britain finally leaves the bloc’s orbit, European Commission President Ursula von der Leyen was also downbeat, saying it would be “very challenging” to overcome the “big differences” that remained. Both sides have called on the other to shift position to try to safeguard almost a trillion dollars worth of trade from tariffs and quotas when a so-called transition period ends on Dec. 31. Since Britain left the EU in January, the talks have been largely hamstrung over two issues - the bloc’s fishing rights in British waters and on creating a so-called level playing field providing fair competition rules for both sides. After a call between Johnson and von der Leyen to take stock on the talks, a spokesman for the British leader said: “The prime minister underlined that the negotiations were now in a serious situation.” “Time was very short and it now looked very likely that agreement would not be reached unless the EU position changed substantially,” the spokesman added. “... He said that if no agreement could be reached, the UK and the EU would part as friends, with the UK trading with the EU on Australian-style terms.” Australia does not have a free trade agreement with the EU and most of their trade is on World Trade Organization rules.