I would like to know what is the fastest speed dialing cordless DECT
phone currently on sale in the United Kingdom and whether its speed
compares to the speed often heard on television shows/movies.

I am referring specifically to the time it takes the telephone to dial
a telephone number once a speed dial number button is pressed; some
phones use a longer delay between the digits while others are faster.
In the movies/tv you hear VERY fast dialing when someone dials a
number on speed dial and I would like to know if such telephones exist
and are available for purchase in the UK.

The maximum speed for dialling is limited by technical standards to
ensure that the phone does not dial too quickly for the exchange. I
think in the movies they speed this up (and omit some of the digits)
to avoid wasting time.

People are rarely on the WC when the phone rings in movies, too :-)

Owain