Dive lamp specialist Light & Motion certainly has the best credentials for producing UK weatherproof bike lamps. This simple 13W Halogen system comes well sealed, with big head gasket and a super secure plug into the rubber-ended battery.
Light output is on a par with single high power LEDs, with a broad even glow for plenty of confidence. The yellowy halogen light doesn't pick out detail well, but glares less in any wet weather. The offset bracket, with its separate tilt and swivel features, is super adjustable but is actually bulkier than the lamp.
The NiMh battery is also relatively bulky, although L&M has kept the single strap hardcase design as smooth and frame-friendly as possible. The super long flex can be a gaff to wrap up when you're not using it on your head (helmet mount is included) but it certainly won't unplug accidentally on you.
Price is competitive with other Halogen units, but weight is high compared to the latest LED rivals.