Taxis are now reliable.  You may try Karwa taxi & limo service tel. 44588888 but book in advance to give them chance to locate you. It has a fleet of cars and drivers and a call centre.  I use them quite often and satisfied with their service.  Another one is Sydney tel. 44449050 which is the official taxi and limo service of City Centre.  Both car companies are reliable and their taxis have meters. A long time and experienced limo and rent a car service is Fox.  It's important that the driver is able to find you and comes on time.