I would have thought that you couldn't cross-examine your own witness, not through judicial fiat, but through definition of the term. The legal definition, per AHD4 is:

To question (a witness already examined by the opposing side).

http://www.bartleby.com/61/29/C0762900.html

This would be the case for a witness called by the opposing side. If you wish to further question your own witness after he has been cross-examined by the opposition it is called redirect examination.

http://www.bartleby.com/61/17/R0101700.html

A hostile witness is one that is unsympathetic to your cause and for whom you get permission from the court to question in a more confrontational manner than is normally allowed. This, at least, is the case in US jurisprudence. Whether the same is true for British jurisprudence I do not know.