Why is it called fly-tipping?

It is called fly-tipping because "tipping" is the old word for dumping a load, the way a tipper lorry tips its back, and "fly" is generally taken from "on the fly": done quickly, on the move, without stopping. Put together, fly-tipping is tipping a load and flying off, which is exactly what it describes: waste dumped from a van or car on a verge, in a lay-by or on a street corner, and the dumper gone before anyone sees. The term is British; elsewhere it is called illegal dumping. In law it is an offence under section 33 of the Environmental Protection Act 1990, and a business whose waste ends up fly-tipped by an unregistered collector can be prosecuted too.