LONDON (Reuters) - Political impetus is required for Brexit trade talks to make progress but a deal may still not be possible, a British government source said on the eve of a meeting between Prime Minister Boris Johnson and the EU’s Ursula von der Leyen. “It’s clear that some political impetus will be required for the talks to make any more progress,” the source said. “If we can make progress at a political level it may allow (Britain’s chief negotiator) Lord Frost and his team to resume negotiations over the coming days.” Johnson will meet von der Leyen, head of the European Union executive, for dinner in Brussels on Wednesday to try and close gaps.