In an article in the Guardian  http://www.guardian.co.uk/uk/2011/jan/19/protest-groups-undercover-mark-kennedy Jon Murphy, an ACPO spokesman, in claiming that the police would welcome an independent body to monitor their use of undercover cops (only to reassure the public, not because they're not regulating their use properly themselves!) said:

"Historically, there appears to have been a reluctance for anybody else to take a role in the authorisation of undercover officers and informants in circumstances where they may be required to commit crimes in order to achieve the legitimate aims of the government."

It's telling that ACPO appear to believe that the police's job is to "achieve the legitimate aims of the government" (and to commit crime doing so), not actually prevent crime and protect the public.

Mr Murphy might want to compare notes with his boss, Sir Hugh Orde, president of ACPO, who recently said it was crucial that police do not appear to be "an arm of the state" who are being used to allow the government to "impose cuts".  http://www.guardian.co.uk/uk/2010/dec/10/police-tuition-fees-protests-orde