LONDON (Reuters) - Britain urged the Hong Kong and Beijing authorities to stop their campaigns to stifle opposition, issuing a statement on Wednesday as three Hong Kong activists including Joshua Wong began their prison sentences. “Prosecution decisions must be fair and impartial, and the rights and freedoms of people in Hong Kong must be upheld,” said Britain’s foreign minister Dominic Raab. Reporting by Kate Holton, writing by Sarah Young, editing by Estelle Shirbon