Looks like the SoS has made a determination after all
"…The date was changed by the Minister for Employment on 11 December 2017 on behalf of the Secretary of State, in a decision made under Regulation 4 of the Universal Credit (Transitional Provisions) Regulations 2014. This supersedes a previous decision made by the Minister for Employment on 26 September 2017.
The Determination also covers the closure of Universal Credit Live Service for new claimants from 1 January 2018."
https://www.gov.uk/government/publications/welfare-reform-act-2012-regulations/welfare-reform-act-2012-regulations
