Declining Concentration in UK Manufacturing? A problem of measurement

It has become conventional wisdom that market concentration in the UK has fallen over recent history. However, the typical assumption has been that all imports are competitive so that any increase in import penetration implies a decline in market concentration. In a world of transnationally organized production and trade this would seem an inappropriate working assumption. Our analysis of the UK market for cars, vans, trucks and buses, where the necessary detailed firm data is available, supports this contention: an accurate assessment of who controls imports is crucial in the measurement of market concentration.