(FILES) In this file photo taken on March 29, 2017 Britain's ambassador to the EU Tim Barrow delivers British Prime Minister Theresa May's formal notice of the UK's intention to leave the bloc under Article 50 of the EU's Lisbon Treaty to European Council President Donald Tusk in Brussels on March 29, 2017. - Severing a truculent partnership stretching back five decades, Britain finally went its own way late Thursday four-and-a-half years after its shock referendum verdict in favour of divorcing the EU. Brexit became reality as Big Ben struck 11:00 pm (2300 GMT) in central London, just as most of the European mainland ushered in 2021 at midnight. (Photo by Emmanuel DUNAND / POOL / AFP)