You can book a taxi via following methods:
Online: http://londonblacktaxitours.net/
Telephone: +44 203 004 4953
Yes, it's possible to pre-book a taxi with London Black Taxi Tours, please contact the company.
London Black Taxi Tours has both regular and air-conditioned taxis, please mention your preference at the time of booking.
Please contact the company on their helpline number to make any changes.
Generally drivers will meet the passengers at the arrivals on airport pick ups but do check with the company.