Prof. Kathryn Sutherland of the University of Oxford has been working on a project to digitise and make available online the surviving manuscripts of Jane Austen's novels.
According to Prof. Sutherland, Jane Austen had a regional accent, ‘She wrote "tomatoes" as "tomatas" and "arraroot" for "arrowroot" - peculiarities of spelling that reflect Austen's regional accent …. In some of her writing, her Hampshire accent is very strong. She had an Archers-like voice with a definite Hampshire burr.’
Well, of course she had a regional accent. Everyone must have had a regional accent, back then. There was no BBC around two hundred years ago to show people how they were ‘supposed’ to speak. Other than, perhaps, the Welsh or Scottish accents of transient drovers or harvest workers, most people outside London and other big cities would only hear speech similar to their own.
Fifty years before Jane Austen was born, Daniel Defoe wrote of Somerset ‘when we are come this length from London, the dialect of the English tongue, or the country way of expressing themselves, is not easily understood, it is so strangely altered. It is true, that it is so in many parts of England besides, but in none in so gross a degree as in this part.… Tho' the tongue be all meer natural English, yet those that are but a little acquainted with them, cannot understand one half of what they say.’
Prime Minister Sir Robert Peel (1788-1850) spoke with a Lancashire accent, despite having been educated at Harrow and Oxford.
So Miss Deborah and Miss Matty probably did not sound like Dame Eileen and Dame Judi. Jane Eyre probably had a Yorkshire accent (her creator apparently had an Irish accent, picked up from her Irish father). And historical novelists should not necessarily imagine that anyone who wasn’t a servant or a labourer spoke standard BBC English.