On Thursday, 18 July 2019 23:29:53 UTC+1, Tricky Dicky wrote:
In the garage I am using PVC trunking ...

The fire retaining cable clips do not have to be within the trunking.

Builder's perforated band round the outside of the trunking will support the cables (and trunking) in the event of a fire.

Spacing has to be sufficient to stop the cables becoming an entanglement hazard. Along a wall every 1m or 1.5m may be sufficient, and each side of a doorway (more over a garage vehicular door).

Owain