Hold on here. The Shire was NOT meant to be a representation of middle England (or England itself, or a representation or anything). This is a common misconception among fans. Tolkien confessed to MODELLING some aspects of the Shire on rural England (a village in Warwickshire, to be precise), but he also patently denied that there was any direct connection between the Shire and England. The Shire is not a metaphor for England, or an allegory.

In letter 154 Tolkien mentions this in passing:

  "...The Shire-hobbits have no very great need of metals,
  but the Dwarfs are agents; and in the east of the Mountains
  of Lune are some of their mines (as shown in the earlier
  legends): no doubt, the reason, or one of them, for their
  often crossing the Shire.  Some of the modernities found
  among them (I think especially of umbrellas) are
  probably, I think certainly, a mistake, of the same order
  as their silly names, and tolerable with them only as a
  deliberate 'anglicization' to point the contrast between
  them and other peoples in the most familiar terms...."

In letter 178 we find him gently correcting a reader on how to address him and commenting on the Shire:

  "By the way, there is no need to alter 'Mr' to Professor.  In
  proper Oxford tradition professor is not a title of address --
  or was not, though the habit has drifted in from places where
  'professors' are powerful little domestic potentates.  I am
  sure that without 'professor' I should have heard less about
  my donnishness, and no one would have said 'The Shire is not
  far from North Oxford.'  It is in fact more or less a
  Warwickshire village of about the period of the Diamond
  Jubilee -- that is as far away as the Third Age from that
  depressing and perfectly characterless straggle of houses
  north of old Oxford, which has not even a postal existence."

In letter 181 Tolkien wrote:

  "There is no special reference to England in the 'Shire' --
  except of course that as an Englishman brought up in an
  'almost rural' village of Warwickshire on the edge of the
  prosperous bourgeoisie of Birmingham (about the time of
  the Diamond Jubilee!) I take my models like anyone else --
  from such 'life' as I know.  But there is no post-war
  reference.  I am not a 'socialist' in any sense -- being
  averse to 'planning' (as must be plain) most of all because
  the 'planners', when they acquire power, become so bad --
  but I would not say that we had to suffer the malice of
  Sharkey and his Ruffians here.  Though the spirit of
  'Isengard', if not of Mordor, is of course always cropping
  up...."

It appears that many people are overly influenced by what Tolkien wrote in letter 190, where he discussed a translator's work:

  "I presume that if I had presented the Hobbits as speaking
  Italian, Russian, Chinese, or what you will, he would have
  left the names alone.  Or, if I had pretended 'the Shire'
  was some fictitious Loamshire of actual England.  Yet
  actually in an imaginary country and period, as this one,
  coherently made, the nomenclature is a more important element
  than in an 'historical' novel.  But, of course, if we drop
  the 'fiction' of long ago, 'The Shire' is based on rural
  England and not any other country in the world -- least
  perhaps of any in Europe on Holland, which is topographically
  wholly dissimilar.  (In fact so different is it, that in
  spite of the affinity of its language, and in many respects
  of its idiom, specially unsuitable for the purpose.)  The
  toponymy of The Shire, to take the first list, is a
  'parody' of that of rural England, in much the same sense
  as are its inhabitants: they go together and are meant to.
  After all the book is English, and by an Englishman, and
  presumably even those who wish its narrative and dialogue
  turned into an idiom that they understand, will not ask
  of a translator that he should deliberately attempt to destroy
  the local colour...."

Tolkien was speaking of the model he used -- he wasn't saying that the Shire should be identified with England. The Shire isn't England, it's an imaginary land inhabited by an imaginary people. The parodies of England and its people are to be appreciated by those people but should not be confused as a statement of identification.

The only real identification Tolkien offered was of the village where he lived when he was young, as again he mentions in letter 213:

  "...And there are a few basic facts, which however daily
  expressed, are really significant.  For instance I was
  born in 1892 and lived for my early years in 'the Shire' in
  a pre-mechanical age...."

If we must be sticklers for detail, then we should say the Shire was modelled on a village in Warwickshire, that the Shire's hobbits are a parody of rural English folk from Tolkien's experience, and that he modelled the place-names on English naming conventions. But that's about as far as it goes. England, even in Tolkien's time, was far more than a village in Warwickshire (in his experience and view).

It would not be an oversimplification in the least to say that the Shire is a representation of a place Tolkien remembered fondly from his childhood -- an English place, but not all of England.

I'm not sure if that SHOULD affect one's opinion of what would be appropriate accents for a movie adaptation, except possibly in that American accents thrown in gratuitously would sound out-of-place (particularly in the mouths of hobbits) for all of us.

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Parma Endorion: Essays On Middle-earth, Revised Edition