Those words have been taken out of context for a start & it's about becoming resilient to the changing threats.
There isn't a specific nuclear threat but there is likely to be widespread, co ordinate cyber attacks.
If you went into M&S after the incident there it was carnage - bo products on the shelves, payments & ordering systems down, website down. The supply chain ground to a halt with effects lasting weeks.
Imagine that but taking out the entire food supply chain, leaving all retailers with the same empty shelves, or taking out the entire electronic payment system leaving people unable to purchase fuel or food or other essentials.
A cyber attack on utilities is also possible leaving a widespread part of the country with no electricity or no water
The government & country as a whole need to be prepared for how to respond.
It's sensible advice to have a couple of days food & water & some cash.
Think through the effect of having no electricity, water, access to shops or transport or internet or combinations of all those for a few days & prepare for that.
I live out in the sticks so have frequent power cuts & always the last to get re connected. I would say an fm radio & torches with spare batteries & a clock. It was very disorientating not having electronic devices to tell the time.