There is a difference between "waste" and "scrap". The waste carriers licence,which would apply to any tradesman,carrying waste generated partly or wholly as a result of paid work.
There is a separate "scrap collection licence" which applies to the collection and transport of scrap,from others,for reward or as part of a business.
If the scrap is yours,which it becomes when the customer allows,and you are not sharing or handing over the cash,then you can weigh it in,in the same way any member of the public can,subject to the recyclers' registration policy,and any HMRC directives concerning income/benefits in kind etc.
There are many,many scare stories,mainly generated by those with an agenda,regarding rules,regs,that are supposedly forced upon us,by either a nanny-state,or more recently,the EU...
Many are attempts at curing problems,the people i refer to above,are whinging about also. Some are safety related,others are purely financial.
A good example is the HGV industry. To look at what is required,as driver,including all the add-ons,licences and tickets...you would not bother.
I have kept my licence,as now and again,i require to use or drive such items. It may be a low-loader,crane,access platform or horsebox.
I escape many of the requirements,employed drivers have,as the law allows this. There are many exemptions,such as demonstration,repair,emergency etc which if apply,negate further permissions.
...So cheer up...i have had very little medical training,and never studied as a doctor...but i cut the cord,on both my sons,and i haven't been arrested yet :coolgleamA: