Was just overtaken by an estate car, belching black smoke behind itself. In the UK, you can't report this to the DVLA, you just have to (literally) suck it up.
It was a 2007 model diesel, and it's only 28 more days until the ULEZ starts around here - it can't come soon enough. ULEZ will rapidly reduce the number of highly polluting old cars like this in our neighbourhood.