In the postwar period, a significant number of politicians (Edward Heath, Margaret Thatcher, and Roy Jenkins) thought it necessary to shed their 'regional' accents and acquire an RP accent. Evidently, this rule did not apply in many other cases, such as David Lloyd George (whose first language was Welsh), Ramsay MacDonald, Aneurin Bevan, Ernest Bevin and Herbert Morrison. It could be argued that this tendency was only ever really relevant to the Conservative Party, and was finally put to rest by Harold Wilson's first election victory in 1964, which marked the official 'acceptability' of English 'regional' accents for the first time in political life (although it is rumoured that Gladstone had a Liverpudlian accent: unfortunately, no recordings exist to confirm this assertion).
Over the past quarter century, a curious inversion has taken place. Blair, Cameron, Osborne and Clegg (all products of public schools) have felt the need to conceal their privileged origins by dropping their consonants. Nobody is fooled by this. Inequality and privilege have become entrenched and have solidified, but the holders of these advantages know that there is a need to conceal them. Some attempt, however transparent and ridiculous, must be made to bridge the gap between these uncomfortable realities and the pervasive rhetoric of 'meritocracy' and 'social mobility'. These people must not show themselves to be overtly posh and entitled, even though they (and we) know that they are. They need us to collude in this collective delusion. Johnson's end-of-the-pier Bertie Wooster impression is not a departure from this, but a development of the same illusion and collusion. 'All this upper-class twit stuff is just one jolly joke', but we know, and he knows, that it isn't. Johnson's 'performance' throughout his entire political career gives the concept of 'bread and circuses' an even more disturbing meaning.