LONDON Net migration to the UK last year was around 20% lower than previously thought, according to revised figures that show a faster-than-expected fall in arrivals and a much larger outflow of British citizens. New data from the Office for National Statistics (ONS) released on Tuesday follows a major overhaul of the UK’s migration measurement system. Officials said most of the revisions stem from adopting labor records, which capture the movements of British nationals far more accurately than