Britain today is still a society in many ways defined by class, but in the 1950s divisions were far more rigid. The 'new wave' films and the sources that inspired them gave a voice to a working-class that was for the first time gaining some economic power.
Previously, working-class characters in British cinema had largely been used for comic effect or as 'salt of the earth' cannon fodder. Here we see their lives at the centre of the action. That action, such as it is, details everyday dramas - hence 'the kitchen sink' tag. We see events through the emotional journeys of the characters.
Interestingly, only Room at the Top (d. Jack Clayton, 1958) and Look Back in Anger (d. Tony Richardson, 1959) look directly at conflict between working-class and middle-class characters.
The later films concentrate on conflicts within the working-class contrasting 'rough' (the very poor, unskilled, criminal and hedonistic - represented by characters like Arthur Seaton in Saturday Night and Sunday Morning (d. Karel Reisz, 1960) and Colin Smith and The Loneliness of the Long Distance Runner, d. Richardson, 1962) with 'respectable' (skilled, aspirational, educated and 'moral' - such as the heroes of John Schlesinger's films: Vic Brown in A Kind of Loving (1962) and the life that Billy Fisher in Billy Liar (1963) appears to lead).
The debates around class are complex. There is recognition that social change and affluence will make the system more fluid. There is also an understanding that the essentials of power will not change - the mindset that reinforces divisions is still very much there.