Park(ing) Day is next Friday

One of my favourite green campaign ideas is taking place on Friday next week. Parking Day highlights the wastefulness of using a car and the land that is needed to keep them.

It started in America but is a worldwide event where people use (after buying a ticket) metered parking spaces and create temporary miniature gardens, parks and other conceptual spaces in the Parking Space.

Wonder what the legal status is in the UK of using a parking space for something other than a motor vehicle?

More info about the event at the Parking Day web site:
parkingday.org