Thank you for the detailed response! Did you get the 41 x 41 x 2.5mm or the 41 x 21 x 2.5mm? Not sure if the 41 x 41 x 2.5 will be enough to tuck some cables inside. I'm thinking of getting 3 x 1.5m having them equally distributed from the middle to the back of the worktop. Originally, I was looking for slotted angle iron, however I cannot believe how expensive they are in comparison to the prices in the US!A few dome-head screws and 25mm outer diameter washers from Screwfix. One in every third slot.
It's holding up well, incredibly sturdy - can't see it going anywhere soon
Here's what I went with: