Priority Black Taxi service for wheelchair users

As a carer for a wheelchair bound client I have found one of the biggest frustrations is needing to call a taxi that is willing to pick up a passenger in a wheelchair.
We have been left waiting for over an hour on many occasions whilst the taxi drivers are actively declining picking us up.
We have been told that wheelchairs are supposed to be a priority but this is clearly not the case. It is not due to a shortage of black taxis as we were told there were five out at that time but that the job was coming back declined one can only assume because of the extra effort needed.
The client I care for who has cerebal palsy has on one occasion been reduced to tears after we was left waiting so long in the cold she bagan to need the toilet urgently and this caused her immense distress.
Weather an appointment or a day out it is becoming increasingly harder to find drivers wanting to pick us up and this is having a negative impact on the quality of time spent out and on the wheelchair users emotional well being.
It should not be ok should to discriminate and, the company policy of AC cabs etc should make wheelchairs a top priority when it comes to black cabs.