You can book a taxi via following methods:
Online: http://www.taxi-londra.com/
Telephone: +44 389 929 3057
Email: taxi@taxi-londra.com
Yes, it's possible to pre-book a taxi with Exapad, please contact the company.
Exapad 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.