Rear Lights Advice

[Sam250]

I'm a fairly new rider of a Yamaha YBR 125. I, perhaps incorrectly, understand the UK lighting requirements like this: there be must be some rear illumination which keeps the licence plate lit at all times, and a rear brake light that activates when either brake is engaged. Recently at night a motorist pulled up to me at a red light to tell me my rear lights are out. Sure enough when I checked I found the headlight will always come on with the ignition but there is no always running light at the rear, only a brake light that shines red backwards and white downwards toward the licence plate, and a red reflector. When I took off the light cover I found there was only one bulb (and socket) for the rear of the bike (the cover is red on the back and clear underneath). This isn't what I was expecting, because surely I can't have a running light and a brake light with this set up. But I am quite new to motor vehicles and if I am misunderstanding something I hope somebody will guide me. I am most concerned that it is not legal to ride on UK roads without rear illumination. And if it is, am I going to keep getting hailed by well intentioned motorists, as happened a second time already!

Edited January 10, 2015 by Sam250

[Stu]

its a dual filament bulb

replace it and see if a new one works

if you look in the bulb you will see the two filaments

[Sam250]

The more you know! Many thanks.