Soundbreaker, they'd probably be told not to do it again and be given £100 from the 'poor box' and sent on an all-expenses trip to Spain, because of their 'deprived' upbringing.
The Arresting Officer, on the other hand, would probably be suspended, investigated, and prosecuted for 'infringing their Human Rights' (won by whom, pray tell?), kidnapping (by removing them to the police station against their will), threatening behaviour (by raising his voice to them) and child molestation (by restraining them when they: tried to run away/broke a beer bottle over his head/stabbed him with a knife/ hit him with a baseball bat*).
God help him if any of the miscreants happened to be a girl! He'd additionally be charged with public exposure, sexual assault and committing an act of gross indecency – because 'little girl chavs' never lie to get themselves out of trouble, do they?
He would, of course, be found guilty, fired, imprisoned for 60 yrs and put on the sex-offenders register for the rest of his life!
On the other hand, I suspect that (given the time-frame when it was conducted and the nature of the materials used) this 'vandalism', although reprehensible and disrespectful, owes more to Halloween pranks than real spitefulness. I am no 'hug a hoodie' Lefty at all and I revere the memory of the guys who took part on the Dams Raid. Nonetheless, the cleaning of the memorial (with toothbrushes perhaps?) – in the full public gaze and publicity would probably be sufficient.
Or we could confiscate their iPods….now THAT really would hit them hard!
*delete as applicable