You use the small claims track of the county court to sue them for the damage they have caused by preventing your use of your parking spaces. You have to assess this 'reasonably' and 'realistically'. It isn't the cost of paid for street or carpark parking in the locality. It is the cost to the businesses in time and inconvenience of being prevented from using their parking spaces.

For example, if this led to an estate agent being late for an appointment and losing a sale you could even consider suing the inconsiderate parker for the loss of the commission on that sale. You might need photographs of the inconsiderately parked cars and a court order to force the DVLA to release the registered keeper's details. I would put up a notice: "WARNING: These business parking spaces are in continuous use. Any unauthorised impeding of them or use of them will result in County Court action for the damages the business suffered as a result. These damages could be £20 to £1,000 depending on the circumstances."