After the debacle over the police tactics at the student protests, culminating in protesters needing brain surgery and being charged at on horseback, the Met may have wished for a quieter 2011. But early signs are that they'll get no such respite, as undercover policing is the latest tactic to come under scrutiny.
The concern isn't about police working undercover, people know that this happens and accept it. But in this case, the group in question were not a serious threat, it was civil disobedience, not hardcore criminal activity that they were engaging in. And more worryingly was the extent that it appears in some cases the undercover officers are acting as agent provocateurs, inciting otherwise peaceful protest into violence so as to give the appearance of a successful mission.
No-one is calling for an end to all undercover policing, but it does need reviewing, and hard questions have to be asked about when it is being used, and who is protecting the public's right to protest.
There's a good summary of the different points here on the BBC.