They must not have a recording from the video feeds showing the pumps on the monitor to the left of the cash register. If they did they might be able to get some plate numbers...but the plates are probably tucked under and not in sight anyway.
If the police really want to end these types of group rides (i'm talking the huge US style biker mob ones) they just need to some under cover work.
Go to the next meet and just blend in with everyone. Walk around and take a boat load of pics of everyone there. Selfies with as many riders as possible as close to their rides as possible. You know for instagram and what not
GoPro everything from the ride with a couple cameras on the bike, one on the helmet. Again for social media and what not. The cameras wouldn't even look out of place, it's expected at these things.
Will this happen? I doubt the police have the resources to spare to do this. If some nefarious shut goes down on one of these rides then it will become a priority.
If the police really want to end these types of group rides (i'm talking the huge US style biker mob ones) they just need to some under cover work.
Go to the next meet and just blend in with everyone. Walk around and take a boat load of pics of everyone there. Selfies with as many riders as possible as close to their rides as possible. You know for instagram and what not

Will this happen? I doubt the police have the resources to spare to do this. If some nefarious shut goes down on one of these rides then it will become a priority.