BRUSSELS (Reuters) - The European Union’s chief Brexit negotiator Michel Barnier was “rather downbeat” about the prospects of sealing a new trade deal with Britain in a briefing for the bloc’s national ambassadors in Brussels on Monday, a senior EU diplomat said. The diplomat, who was at the briefing, said Barnier told the envoys that differences between the EU and London persisted on the three main issues that have long divided them, and that the ball was now in British Prime Minister Boris Johnson’s court.