A landlord can't give their tenant a valid section 21 notice if the landlord has not previously provided the tenant with written information about the deposit and the scheme, the gas safety certificate, energy performance certificate (EPC) and the government's How to Rent guide. Where in the statutes are each of these respective stipulations to be found, and in what format must each of those documents be served in in order to be valid?
For example, user @Lag has opined that it seems that a gas safety certificate perhaps ought to be on its original paper. Any case law citations as well as statutory ones are very welcome!
The earlier incarnation of this question included and garnered some informative research links, which are collected below:
Serving mandated accompanying materials to an eviction notice by email
https://landlordlawblog.co.uk/2017/01/17/why-not-serving-notices-properly-can-cost-you-your-case/
https://www.duttongregory.co.uk/site/blog/duttongregorynews/beware-of-service-of-notice-by-email
See the earlier incarnation of the question for some slightly more convoluted excerpts and commentary on these resources.