I think I've discovered why there's been a rash of bikes with either red light at front and back, or white light at front and back. These are mainly, but not always, to be found adorning pavement cycles. It appears that our local pound shop has taken delivery of a consignment of mis-packaged bike lights. Each packet either has 2 red lights, or 2 white lights. To kit your bike out properly - you have to spend £2... (and then pass a set on to your mate)