Hi,
Whilst reportedly, a HHC officer would rarely use their powers of office outside of their usual remit (just how a HMP Warden wouldn't), the HHC differ to other 'Parks police' as the Act below still applies - uniquely - to those officers in HHC.
"Section 16, Corporation of London Open Spaces Act 1878
Every reeve, assistant reeve, bailiff and keeper and other officer appointed by the Corporation from time to time for securing the better execution of their said powers, regulations and bye laws shall have all the powers and privileges and be liable to all such duties and responsibilities as any police constable has and is liable to within the police district in which the common, commonable land or open space, in relation to all or any part whereof such reeve or other officer, is situate: Provided always, that no such officer shall act as a Police Constable unless he is in uniform, or, if in plain clothes, shall be provided with his warrant."
Again, they are commissioned by the CoLC in the same way that the CoLP are, they have CoLP plate badges, they have the same red chequers as CoLP, all of their operational kit is supplied by the CoLP and, by all accounts, they have the same powers as a CoLP officer. However, yes, you're right about serious offences being handed to the MET... HHC is barely a handful of officers and CoLP are <1000. Warwickshire Police is the smallest county police force and they themselves often rely on surrounding forces. In fact, I think they're now in cahoots with West Mercia Police?
Sam