UN Working Group of human rights experts condemned UK's racism report, calling review 'reprehensible'
Body accused report of effectively whitewashing history of slavery and colonialism, and 'falsified facts'
UN said review by commission founded by Boris Johnson 'repackages racist tropes and stereotypes into fact'
Commission on Race and Ethnic Disparities said UK racial diversity should make country model for others
Downing Street rejected the criticism, with PM's spokesman insisting 'we remain proud of UK history'