The issue of migrant workers’ organising and integration into trade unions in the UK as well as in other European countries has been considered only marginally. The British industrial relations tradition tends to frame workers with migrant background in terms of ‘ethnic minorities’ to be organised as a (national specific) separate group or as simply workers member of industry-based branches. This paper aims to supersede this approach by providing an original comparison of the strategies of three major UK unions (Unison, Unite, GMB) to include migrant workers in their structures at a time of critical change in labour migration into the country. Our comparative approach across national unions allows us to highlight limits and potentials of ongoing experiments by trade unions attempting to change their structures, policies and coalition strategies to respond to those among the most compelling challenges of our global times: the growing mobility of labour and the increasing fragmentation, diversification and precarious nature of the workforce.