You can book a taxi via following methods:
Online: http://www.swallow-cars.co.uk/
Telephone: +44 199 244 2844
Yes, it's possible to pre-book a taxi with Swallow Cars, please contact the company.
Swallow Cars 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 contact the passengers to arrange a convenient place to meet on airport pick ups but do check with the company.