The Windrush saga in the British media has thrown light on the situation of post-WW2 migrants from the British Empire - particularly the Caribbean, India and Pakistan - who came to the UK in the immediate aftermath of WW2 under the Attlee government and so began modern British immigration.
My question is - why did these migrants come in at that time in particular, and why had they not come previously? Most of the now-ageing immigrants describe having thought of themselves as British subjects, and therefore eligible to move throughout the Empire. And indeed, some migrants did move to the UK during the earlier part of the Imperial era. As early as 1892, an Indian migrant was elected to the House of Commons, and there were a number of notable individual Black/Asian people living in the UK in the 19th Century, as well as small communities in certain specific places. I cannot find any references to restrictions on Empire/Commonwealth migrants prior to the Commonwealth Immigration Act of 1962.
My question is - why did substantial numbers of Empire immigrants not move to the UK during the earlier periods of Imperial history, and why did so many come in at that particular point in time? I am vaguely aware that it was partly because the socialist Attlee government actively encouraged them to come, but I would have thought that, given the substantial disparity in GDP per capita between Britain and some of the other nations of the Empire, there would have been significant pull factors in place previously anyway. Also, what were the motivations (ideological and practical) for the Attlee government in encouraging their arrival?