Hi Darren, and welcome to another fellow Brit! [Linked Image]

Most people here associate red and black with positive and negative respectively of a DC circuit, but there are variations.

In the days when DC mains supplies were still around in Britain, the IEE specified the following:

Positive of 2-wire circuit => Red
Negative of 2-wire circuit => Black

Positive of 3-wire circuit => Red
Neutral of 3-wire circuit => Black
Negative of 3-wire circuit => Blue

Outer (positive or negative) of a 2-wire circuit derived from a 3-wire system => Red

In the typical residential street where half the houses were fed from the positive side of a 3-wire DC system and half from the negative side, it meant that for the latter houses the red would actually be the (live) negative, with black as the (earthed) positive.

The IEE specification of blue for a live negative wire in a 3-wire circuit dates back only to 1966. Prior to that, they specified that the 3-wire negative be yellow or white, (i.e. the same color as the second phase of a 3-phase AC system.)

When the European colors were adopted for flex around 1970, the IEE then specified that flex carrying a 2-wire DC circuit should use brown for positive and blue for negative, in line with AC systems.

The use of red and blue coding for conductors positive or negative with respect to ground was, and indeed still is, found in other areas.

For example, in British telephone exchanges the supply busbars (which are at -50V with respect to earth) are generally identified with blue.

Look on the London Underground and you'll see the feeder equipment at the side of the track identified with red for the positive (outer, +420V) conductor rails and blue for the negative (center, -210V) rails.