You can book a taxi via following methods:
Online: http://www.ukchauffeursltd.co.uk/
Telephone: +44 203 326 0513
Email: bookings@ukcl.net
Yes, it's possible to pre-book a taxi with Lhr Heathrow Transfer Taxi, please contact the company.
Lhr Heathrow Transfer Taxi 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.