yes but as you may have seen in some recent news articles some of these signs are misleading or not clearly displayed.
some private land is not obviously signed ie it could be a layby outside a premises or appear to be a regular council run car park.
footage was shown on a tv news report of clampers hiding behind a wall waiting for unsuspecting prey.
as soon as they had left their vehicle they pounced and then demanded a ridiculous amount of cash for removal of the clamp.
in these cases there was no time period of grace