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My 4 bed 2 storey house was extended 2 years ago and completely re-wired, but I am having to upgrade the insulation and board out the loft myself.

In the loft the electricians clipped the new 1.0 mm wiring to the joists. There’s no ring, no JBs, it’s LED lighting only and all radial feed. No electric showers.
The existing 100mm glass fibre insulation was replaced over it in the original areas, and 300mm placed in the extension

I have been looking into whether there is a safety need to pull out all the cable clips to allow slack for an extra 200mm insulation so that I can lift the wiring over it in the original areas.
The present standard seems to say there isn’t such a need as long as the current doesn’t exceed certain limits, and that it is safe to lay insulation over the cables.
I have been able to find out these limits from the latest BS 7671

According to the attached table if I install insulation as per method 101 that will downrate the cable to 10.5 amps. There are total 11 light points, 2 small fans and a smoke detector system, so I will be well under 10.5 amps.
Advice elsewhere simply says the standard capacity should be downrated by 50%, but that might be an earlier standard.

In summary would I be over-reacting in unclipping all cables, and could this actually cause harm?

You downrate cable current carrying capacity to account for less air flow. Airflow allows any heat to be easily dissipated. As you said you have such a small load it will be your choice what you do.
Do be advised some cables can be damaged if they come into long term contact with polystyrene.

Thank you, I didn't know that about polystyrene but won't be using it anyway. I haven't had any adverse replies so I will go ahead without unclipping the cables.
I wondered what a worst case would be if heat couldn't dissipate.
Without convection there is always conduction and radiation.
Doesn't convection involve conduction as well? Heat has to be transferred to the adjacent air by conduction, and is then convected away.