Due to the change in standard wiring colours in houses a few years back if you see one of these labels on the consumer unit there's no guarantee of what's what.
Extra Large Caution Cable Colour Harmonisation Labels with Diagram are required to clearly indicate that an installation has cable colours to two versions of British Standard 7671. Printed with a clear Full Colour Diagram to illustrate the correct wiring colours, our Extra Large Caution Cable...
www.patlabelsonline.co.uk
Blue can be either live or neutral.
Black can be either live or neutral.
Live can be either red, yellow, grey, brown, black or blue.
Apparently a sticker on the fusebox makes everything dead safe tho