I do not know which area you live in, or which areas you 'collect' in, but according to Google, licenses are required in most UK locals ....
Example I fond:
Overview

A licence is required before any person can collect scrap metal or run a scrap metal site. As the Local Authority we are responsible for issuing the licence.

Please also see our scrap metal licensing policy.
Conditions

There are conditions attached to each licence and these must be adhered to.
Cost

£270.00 Collector licence

£455.00 Site licence