It's sad that people find this necessary. When I was young, myself and all my friends went to elocution lessons. Later on, in school, when reciting poetry or performing classical drama, received pronunciation would be insisted on. People just seemed to accept that our natural accent was objectionable and that 'speaking properly' meant cultivating a different accent.Yeah, that's a neat reversal of the tendency by rustics* to affect a metropolitan accent to make themselves sound posh or whatever.
*No offence intended; I'm a rustic myself.