The reference from the Secretary of State was through a Tweet by the Liaison Officer of the APPG for GA. The LAA incorporated it into their response. I'm not aware of the source to Grant Shapps directly.
The actual legislation governing this lock down is readable here:
The Health Protection (Coronavirus, Restrictions) (England) (No. 4) Regulations 2020
The more simplified guidance is here:
New National Restrictions from 5 November