With Ian Blair stepping down as head o the Metropolitan Police in London, UK because of a lack of support from Boris Johnson, and Norman Bettison from West Yorkshire refusing to even apply because of the potential for political interference:
http://news.bbc.co.uk/1/hi/uk/7651738.stm
policing by consent is under sever pressure in the UK. Getting the political balance right between party political control of policing, and no accountability at all is very difficult. Ian Blair, being an incompetent plank (judging from his defence of the shooting of Jean Charles de Menezes immediately after the event) doesn't help. What this case has shown so far is that the police authority model is not working. It has been unable to effectively deal with Blair over the last couple of years, and now has a highly partisan head of the Authority in Johnson determined to get a tory-leaning chief constable installed in his place.
We do need oversight of the police in London, and maybe the solution is to require a 75% vote in the Greater London Authority (GLA) to hire or dismiss a cheif constable. That would typically require a consensus between the major parties, and stop the likes of Johnson in their tracks. Further, the Chief Constable needs to be able to come to the GLA to censor the mayor for political interference. Again, a 75% vote shoule be able to remove the mayor.