The journalist Peter Wilby makes an interesting point (in a long article about Tony Blair in the Guardian Review) about the huge volume of material written on both Thatcher and Blair while they were still in office – a sharp contrast to previous Prime MInisters. And he provides a helpful snapshot of the trends which have led to this:

More relaxed official attitudes to ministers and civil servants giving interviews to journalists, the rise of the political adviser charged with ensuring that ministers’ views and intentions are understood by the public, the decline of social inhibitions on divulging confidences (or, put another way, the increased acceptability of gossip and tittle-tattle) and the enormous growth of media scrutiny – all these have increased the volume of material available to contemporary biographers and historians.