The focus of the safety monitors is public safety rather than security of supply. They provide a trigger mechanism for taking direct action to avoid a potential gas supply emergency (as defined in the Gas Safety (Management) Regulations).
You can find details relating to the current levels of storage within the "Storage & LNG Operator Information" report on the Gas Transmission Operational Data page.
The daily margins notice and safety monitor position update report is published daily below following the 13:00 demand forecast.