SpookyFrank
A cheap source of teeth for aquarium gravel
Hows it aggravated? Unless they are causing damage or disrupting lawful activity and it sounds like P@O announced they weren't running the ferries today anyway so hard to make that stick. Trespass otherwise is civil (thats kind of the pint of the current C&P bill). There may be all sorts of weird Victorian offences relating to ships, a bit like all the odd Railway ones. I can see Kent and Humberside (and Welsh forces if they are affected?) senior plod telling any private security company to do one if they start 'detaining' people in these circumstances.
Besides, anyone who doesn't have crown servant / office holder cover (plod, immigration, screws etc) who starts using handcuffs on people is asking for trouble, in a kind of having to sell your car if not your house kind of way, if it all goes pear shaped - and I'd be really surprised if any insurance company would write a policy for a security guard using any kind of cuffs, especially rigid ones. There is loads of potential for permanently injuring or even killing people pretty quickly if you make even quite small errors.
Aggravated trespass is a criminal offence, and a very vague and easily-abused one at that. But there'll be no trials and probably no charges either; once the workers are off the ships it doesn't matter what pretext was used to remove them.
As for police siding with workers against scab security, that has literally never happened.