This is a case where Link Parking won and were able to show a Judge (DJ Pratt) that the Head Lease did contain the right to vary the parking regime at the location. It shows the need to clearly understand that the relationship between a resident and the parking company is not by virtue of signs in the first instance but whether a lease allows the introduction of a "management" scheme at a later date.
In this case it did but you should always check your paperwork. The key phrase to search for is whether the "landlord is entitled from time to time may introduce regulations with regards to the proper management of the location".
Often in communal residential areas there is a need to bring some form of "management or order for the benefit of all". They usually take the form of a covenant within the lease and it is the lease you must turn to, to see what scope there is to introduce new restrictions such as parking.