In message , at 20:35:59 on Thu, 8 Oct 2015,
tim..... remarked:

As someone else has already remarked (it might have been you),

It was me.

the "pre-booking" does not confer any advantage on anyone (except for
not having to do it close to the time of travel).

The driver will simply be handed a job over his radio. He will
experience no difference as between a pre-booking or one that has
just been rung in by a member of the public. Given that, it's hard to
see why or how a discount for early booking could be expected.

I think it perfectly reasonable when you think you are ringing a
mini-cab firm

The only scenario where pre-booking might be expected to attract a
discount is an "airport run" where the driver can hope that the company
arranges for him to have a fare in both directions. Not unsurprisingly
most companies express this "discount" as a flat-fare to nominated
airports, which is cheaper per mile than a random booking. They can also
quote for different sized vehicles, whereas for normal bookings you'll
just get sent whatever the nearest available one is.

eg:
http://www.panthertaxis.co.uk/index....&view=article&
id=11&Itemid=60
--
Roland Perry