It really doesn’t take a lot of scrap to make up a tonne, and with mixed scrap at £120 tonne, you would only need to make 1 load a day to have a reasonable weekly income. I generate a fair amount of waste metal as machines get broken and repaired, or come to the end of their lives. We used to let a scrappy take stuff, but when he started turning up here with a brand new truck to ask if we had anymore, I looked into it, and realised he had probably had a couple of grands worth of scrap from us in the space of a year. The place is much tidier now though. However, a couple of loads I took in last year netted about £400.
It is however, much harder to just drop something off at the scrappy as you need to show a passport/ID and you only get paid by BACS now. I would imagine there is still a cash for scrap economy out there, but there will be a middle man who pays cash below market value, who then takes it to the official “waste metal recycling centre” and gets paid the proper price for it.