Yes. There is a very stupid convention in the UK whereby some people take flashed headlights to mean "I've seen you, pull out". Flashed headlights should only ever be used as a warning, as they are in sensible countries with no confused sense of politeness and courtesy. However, if Brits are going to flash each other, a quick flash, coupled with obvious slowing down should mean "I've seen you". A sustained flash should mean "I'm coming through". Obviously Daytime Running Lights qualify as sustained flashes. Brits are similarly idiotic about the use of horns. They should only ever be used as a warning. Never as a 'toot, toot' "hello" or "goodbye". And never ever as a rebuke. In sensible countries no one ever takes offence at being tooted as a warning. In Britain 90% of drivers do.