Getting in/out of a black cab

I've slipped and managed to injure my knee and quadriceps muscles. I can no longer bend the injured leg but need to get myself to hospital. I can just about get around if I keep the injured knee in the locked position otherwise the leg just gives way.

Does anyone know if I'd likely be able to get in and out of a black cab? Do all black cabs have the same accessibility features? Thank you.