these will help
https://www.gov.uk/doorstep-selling-regulations
it appies to goods and services over £42 – i think under that value, then you need a pedlars license.
https://www.gov.uk/pedlars-certificate
certain services are exempt from both.
We had a load of recently released / reformed characters selling door-to-door, i queried this on here a while back and i also spoke to local plod about it. Those chaps(esses) will never belong to a “licensed” group as plod discourage it. They are often being used by less scrupulous types to earn money, as the “pedlars” only get a small cut form the proceeds.
I can see why they do it, and sometimes i feel sympathetic about it, however at the same time by allowing it you support the real profiteers!