Got to say that I'm not surprised, although the enforcement aspect will be difficult if large numbers are involved.
We use "Dispersal Notices" effectively for dealing with groups of anti-social youths hanging around intimidating the public. This effectively means that we can move them on, by force if necessary if they are within a particular defined locality. The issue here is that a notice has to be made known publicly and the area it covers defined.
There is a term we use as "within the spirit of the legislation" which is basically using the legislation in circumstances that it was not designed for.
If a group of MG drivers met in a car park for a chat and a coffee, and this legislation was used, it would not be "within the spirit of the legislation". However, to be honest, I support it's use in respect of the mixed marque, hand-brake turn in McDonalds car park brigade on a Saturday night.
I'd be interested in the specific legislation, Act and section, being used.