I agree with CheekyChops. Unless there's some form of agreement between an employer and a trade union about the way that appointments should be filled, an employer is free to determine their own criteria both for appointing new staff and for promoting existing staff.
As long as there's no discrimination which breaches relevant legislation (such as on the grounds of race or sex) an employer is free to give a senior post to the office junior (who can't even make a cup of tea, yet alone do his existing job), promoting him over the heads of a hundred other staff, all of whom are far more experienced, far better qualified and far better at the job than he is. The other staff might not be happy that the promotion wasn't advertised. They'll be even less happy when they find out that their new (untalented, poorly-qualified and inexperienced) boss is the Chairman's nephew but there's absolutely nothing they can do about it. It's perfectly legal.
Chris