The Finance Act 2008 seems to have changed the term 'public road' to 'public place'. The question is whether the public have free unhindered access to the land.
From: http://www.astra-mk2.com/forum/archive/index.php/t-34275.html
2 schools of thought here.
1 - its a public place as the public has "free access" into the land without fences, lockable gates etc
2 - According to http://www.direct.gov.uk/en/Motoring/OwningAVehicle/UntaxedVehicle/DG_069727 "A public road is a road maintained at the public expense, including grass verges and ground adjoining the road. "
However, the legal statute is at http://www.legislation.gov.uk/ukpga/2008/9/schedule/45 - Finance Act 2008
Essentially it says that if the public has access then its not private. However (and I quote)
"This Schedule does not apply to—
(a)any place which is within the curtilage of, or in the vicinity of, a dwelling-house, mobile home or houseboat and which is normally enjoyed with it, or
(b)any place which is within the curtilage of, or in the vicinity of, a building consisting entirely (apart from common parts) of two or more dwellings and which is normally enjoyed only by the occupiers of one or more of those dwellings.”
So they cant come onto your land / driveway to clamp (under a) and they cant clamp in the carpark of a block of flats (under b) but in your case, they probably can clamp as its publically accessable and isnt covered by a or b above.
You might be covered under 2 (b)