When Henry crashes into the phone box both his headlights are clearly intact and there is no serious damage to the panel work. This is also true when he drives off. Shortly after, we see his car has a broken headlight and severe panel damage.
In the restaurant scene towards the beginning of the movie, when The Wilts are having dinner, the waitress comes in and asks if anyone has a 'Y' registration Cavalier and Henry gets up, however, later shots of the same car show it to be an 'X' registration car.