Incidentally, on what you say, the most you did was push a man. To call that common assault, unless the push was aggressive and unusually forceful, is being highly technical and unrealistic as far as prosecuting is concerned, and nobody would bother charging it. You are not being prosecuted on that basis. You are being prosecuted on the basis of the cab driver's version. If that goes out of the window, the magistrates refusing to believe it, or doubting it, then you should be acquitted. Magistrates will not reject the prosecution's case and then start looking for some other technical assault to convict on instead. They convict on how the prosecution put their case, on the basis for the charge, and nothing else