A few thoughts for the Metropolitan Police:
Firstly, people dressed up as zombies do not normally pose a threat to the general public. They are not, in fact, the living dead. Although they may shuffle past you moaning about brains, and may even fake eating each other for a bit of a giggle, the chances of them causing harm to real people are not above average. They are more likely to break into Thriller-style dances than they are to break out into a riot.
Secondly, fancy dress parties in general are, surprisingly, not illegal – even when they happen in public spaces. I know it must be tempting sometimes, especially when you see a really bad Harry Potter costume or a genuinely horrid PVC nurse outfit, but you are not supposed to act as the fashion police. Dressing up is not a crime.
Thirdly, zombies may not be fast, but they can generally shuffle under their own power. Police vans are admittedly much quicker, but arrests are not meant to be used as a way of moving peaceful people out of areas where you don’t want them to be. They’re also not meant to be used to keep London pretty and acceptable while the world’s TV cameras are pointed in our direction. Edit: Nor on people filming arrests and then talking to journalists.
Fourthly, while I understand you can keep better tabs on the living dead when you have them under lock and key, zombies have the same rights as your standard flag-waving patriot. No matter what day it is. We did not turn the law off on Friday. We did not become a dictatorship for 24 hours for the sake of a wedding. Arresting people for acting in ways that are not sanctioned by the establishment is generally not considered to be one of the hallmarks of democracy.
Fifthly, although none of the zombies were charged with any offence, the effect of arrests is to stifle dissent and to scare people into behaving themselves – much like the earlier arrests the night before. There was no violence on Friday and no aggression by this group of zombies towards either the police or the public. No potential weapons or intoxicating substances were found in their bags or on their persons. At best their arrests were disproportionate. At worst they were deliberate intimidation as a consequence of doing something that wasn’t on the official script for the day.
Finally, if sitting in a coffee shop while dressed as a zombie is an offence, I am guilty many times over. And I’ll do it again in future. I will fight for our right to look like idiots while drinking caffeinated beverages, because some things are important.