You can book a taxi via following methods:
Online: http://www.greatbritishtaxis.co.uk/
Telephone: +44 132 770 0011
Yes, it's possible to pre-book a taxi with Great British Taxis Ltd, please contact the company.
Great British Taxis Ltd 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.