I recently bought myself some new cycle lights. They both have a "Flashing " option yet on the assembly instructions that came with them it states that this function is not to be used on public roads.Why then do they have the flashing option if you aren't allowed to use it?
It may be theoretically illegal to use flashing lights on a bicycle, but then isn't it also illegal to ride one at night without lights at all? The town where I live is full of unlit bikes at night - as I suspect is everywhere else in England - but nobody seems to care enough to prosecute. If I were you, I would be lit up like a Chrismas tree with all the flashing lights you can afford, that way you stand less chance of being hit by half blind motorists. (and yes, I drive far more than I cycle, and I do speak from experience of having been knocked off my bike!)
Probably for the same reason you can purchase multipacks of cigarettes in duty-free in sizes so large that you would have to exceed your allowance to carry them with you!