There are two separate issues here:
Bare Ground vs. Anything Else
A bare ground of a particular size is, nominally, no different from an insulated wire of the same size. However, wrapping a length of wire with electrical tape does not provide the same level of protection as manufactured insulation, and is not considered a reliable substitute. Among the problems:
- If you miss a spot when wrapping, you have a real safety problem.
- The ends (and there may be many "ends" as you wrap a long wire) of sections of electrical tape are more prone to catch on screws, other wires, parts of junction boxes, etc. than manufactured insulation
- The thermal and/or electrical properties of electrical tape may be sufficiently different from manufactured insulation to cause a problem
Electrical tape is great for:
- Patching up a nick in the insulation of a wire (ideal is to replace the wire, but that is not always so easy)
- Wrapping around screws on a device (receptacle or switch) to prevent contact with ground wires
- Marking wires for identification (within certain limits)
but not as a replacement for insulation on a length of wire.
Note that ground is the only wire that can be bare. That is because it is also, depending on other factors, often attached to metal boxes & conduit or to appliance frame/casing, all of which are (effectively) "bare metal". All other wires, including neutral wires that are nominally "same as ground", are insulated everywhere.
Changing Colors of Wire
The general issue of changing the color of a wire is an interesting one. The actual colors (except for ground = bare, green or green/yellow) vary significantly by country/region. Using the US as an example (I assume you are in the UK based on reference to Wickes), the normal colors are:
- Neutral = white or gray
- Hot = black, red, blue or any other color except green, green/yellow, white or gray
Within each category, wires can be marked using tape on the ends. For example, you can mark black wires yellow by putting a piece of yellow tape on each end for identification. However, you can't put white tape on black wire (to change hot to neutral) or red tape on white wire (to change neutral to hot). There are some exceptions with cables (e.g., to mark a switched hot), but this is a nearly universal rule.
The end result for your situation is:
- Can't turn a bare wire into hot or neutral by wrapping with tape
- Can't turn a green or green/yellow wire into hot or neutral by marking the ends with tape
You might be able to turn a green or green/yellow wire (i.e., insulated but wrong color) into hot or neutral by wrapping the entire length with an appropriate color of tape (i.e., does not have the "miss a spot" or "maybe not insulated well enough" problems). I wouldn't recommend it, but a UK code guru could give you the answer to that option.