Before Doctor Who returned in 2005, every Doctor, bar Sylvester McCoys Scottish incarnation, spoke with received pronunciation, as everyone would have switched off their telly at the time if a Liverpudlian Time Lord appeared on their screens (even though they did in the form of Tom Baker and Paul McGann, but ssh, dont tell them.) Eccleston, being the utter maverick he is, kept it Northern and stated the obvious that every planet has a North. Tennant ditched his own Scottish-ness for a Micky Flanagan-inspired cockney twang, and Smith... hes a bit posh, isnt it?  Steven Moffat has stated that Capaldi is likely to keep his own Scottish accent, which could alienate over-seas viewers or bring everyone together and rejoice in his soothing pronunciations of the English language. Time will tell.