(FILES) In this file photo taken on June 28, 2016 A man waves both a Union flag and a European flag together on College Green outside The Houses of Parliament at an anti-Brexit protest in central London. - Four and a half years after Britain voted to leave the EU and as eight months of painstaking trade talks reach a climax, Boris Johnson is set on December 13, 2020, to answer the most fundamental question: what is Brexit? Britain left the EU in January and is in a standstill transition period until December 31 while both sides thrash out the terms of their new trading relationship. (Photo by JUSTIN TALLIS / AFP)