Second wave
"School" of playwrights working in the 1960s and 1970s, influenced by sociopolitical changes.
Stage Censorship and Students' Revolt
Until 1968 the representation of violent, blasphemous and sexual improper scenes was censored by the Lord Chamberlain. After this law was abolished young playwrights had more freedom for their original intentions and could show the previous taboos. But it took quite a while until Parliament agreed to do without the Lord Chamberlain's office. The decision-making process was fuelled by three famous plays and one famous theatre scandal: the play was Edward Bond's Saved (1965), which features a scene in which a baby is stoned to death, and could only be shown as club performance. The other two plays are John Osborne's A Patriot for Me (1965) (featuring homosexuality) and Bond's Early Morning (1968) (censored for irreverent depictions of Queen Victoria and her family).
Fringe Theatre
This form of theatre emerged around 1968 and functions as an alternative to the traditional theater because the plays were performed on small stages in the suburbs, basements and factory buildings. This form also influenced the legitimate stage because the fringe theatre created many new talented playwrights [who??], that brought the nearness to the audience and the openness for experimental elements and themes, from the intimate and personal stage on the big stage.
Before the emergence of the fringe theatre, there were almost exclusively male playwrights dominating the English drama scene. After the establishment of this new form, women in the theatre reached more prestige and dramatists like e.g. Caryl Churchill could experiment with gender roles and other "difficult" subjects. In Cloud Nine (1979) for example she showed postmodern permutation of gender roles and debunked the connection between the British colonial mentality and sexual oppression.
References
Innes, Christopher. Modern British Drama 1890-1990. Cambridge: Cambridge University Press, 1992.
Englische Literaturgeschichte. ed. Hans Ulrich Seeber. 4th ed. Stuttgart/Weimar: J.B. Metzler, 2004. p. 392-394.