If parking matters have been de-criminalised in your area (so that 'tickets' are given out by council employees rather than by traffic wardens or the police) contact the relevant council department. (If a vehicle is "parked with one or more wheels on any part of an urban road other than a carriageway (footway parking)" a 'Code 62' parking ticket can be issued/
If you've still got traffic wardens (or police community support officers) enforcing parking around your area, speak to your local community constable. You could even do that anyway, if you'd prefer, since (irrespective of parking legislation) obstructing a public footpath is a criminal offence.
Chris