You can book a taxi via following methods:
Online: http://www.wheelgetyouthere.co.uk/
Telephone: +44 208 568 3366
Yes, it's possible to pre-book a taxi with Wheel Get You There, please contact the company.
Wheel Get You There 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.