In practical terms, I doubt if anything you do will change the decision about this position. Your only legal entitlement would be if you could prove that one of the other applicants for this position was discriminated against on one of the nine grounds mentioned in equality legislation.
However, you may well be able to change the policy for future reference. Is there any channel for staff to raise relevant issues with management, such as a partnership committee, or a union group, or a morale committee. You could get this issue raised, with the suggestion that you don't go through a 'charade' recruitment process in future. If management have chosen one individual for a position, so be it - let's not play games about it. You could choose to try to educate management on the benefits of a fair and open recruitment process, but you'll probably be beating your head against a brick wall.