Stealing copper, getting under older cars and cutting out catalytic converters, yes. Copper is not a big money maker but it's better than collecting aluminum cans.
The problem with 90% of crime is poverty. They do hundreds of dollars of damage to make a few bucks. If we had universal basic income or better safety nets these crimes would nearly vanish overnight.
Well, except that it's nearly always super damaging.
The US version would be more like collecting cans back when they had a 5 or 10 cent deposit. Today I can't really think of anything like that. Maybe driving Uber/Lyft. Or just panhandling/begging.
People do that now in the Netherlands. The bins on the streets of Amsterdam sometimes have little holsters for bottles and tins so you can leave them for people who'd otherwise (or I imagine who still) dig through the rubbish for the deposit.
It's not that £4 cable costs £300. £4 is the scrap value of the copper once the insulation has been peeled off. Freshly made cable costs a bit more than that.
It costs £300 to fix because of the cost of the cable, labour and the workmanship.
Yes. The cables are intentionally made "too thin" so that they weigh less and are less stiff. The upside it it makes handling them much easier. The downside is they they get pretty hot pretty fast, and from there you have two options: Actively cool the cable from inside or throttle charging so the cable doesn't melt.