More notes on Pronunciations of English (lifted from the Cambridge
Encyclopedia of the English Language):

Backgrounder on "THE" accent

In England, one accent  has traditionally stood out above all others in its
ability to convey associations of respectable social standing and a good
education. This "prestige" accent is known as RECEIVED PRONUNCIATION, or
RP. It is associated with the south-east, where most RP-speakers live or
work, but it can be found anywhere in the country. Accents usually tell us
where a person is from; RP tells us only about a person's social or
educational background.

In due course, RP came to sybolize a person's high position in society.
During the 19th century, it became the accent of public schools, such as
Eton and Harrow, and was soon the main sign that a speaker had received a
good education. It spread rapidly throughout the Civil Service of the
British Empire and the armed forces, and became the voice of authority and
power. Because it was a regionally 'neutral' accent, and was thought to be
more widely understood than any regional accent, it came to adopted by the
BBC, when radio broadcasting began in the 1920s. During WW2, it became
linked in many minds with the voice of freedom, and the notion of a "BBC
pronunciation" grew.

Present Day Situationer on "THE" accent

Today, with the breakdown of rigid divisions between social classes and the
development of the mass media, RP is no longer the preserve of a social
elite. It is best described as an "educated" accent - though "accents"
would be more precise, for there are several varieties. The most widely
used is that generally heard on the BBC; but there are also conservative
and trend-setting forms. The former is found in many older establishment
speakers. The latter is usually associated with certain social and
professional groups - in particular, the voice of the London upwardly
mobile ("the Sloane Rangers") in the 1980s.

Early BBC recordings show how much RP has altered over just a few decades,
and they point that no acccent is immune to change, not even 'the best'.
But the most important observation is that RP is no longer as widely used
today as it was 50 years ago. It is still the standard accent of the Royal
Family, Parliament, the Church of England, the High Courts, and other
national institutions; but less than 3 per cent of the British people speak
it in a pure form now. Most educated people have developed an accent which
is a mixture of RP and various regional characteristics -'modified RP',
some call it.

Nonetheless RP continues to retain considerable status. It has long been
the chief accent taught to foreigners who wish to learn a British model,
and is thus widely used abroad (by far more peole, in fact, than have it as
a mother-tounge accent in the UK).