What is the best option for painting a window that is 8m - 9m off the ground? Does a tradesman need a license/insurance to operate a cherry picker?

Yes, a cherry picker operator should be trained and hold an IPAF card (Industrial Powered Access Federation). Also worth checking he/she has public liability as if the cherry picker is on your land or property and something falls from height and causes damage or hurts someone below, you may end up being held liable for negligence.

Get a window fitter out to change it to upvc, no more painting, and might be cheaper than a cherry picker. Otherwise I have seen the opening sashes taken out, lean out to paint frames, paint the sashes inside then refit when dry.