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(FILES) In this file photo taken on March 28, 2017 Britain's Prime Minister Theresa May, signs the official letter to European Council President Donald Tusk, invoking Article 50 and signalling the United Kingdom's intention to leave the EU, in the cabinet office inside 10 Downing Street on March 28, 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 CHRISTOPHER FURLONG / POOL / AFP)