Take this with a pinch of salt.
The normal daytime population of mandarins in Whitehall tends to drop quite dramatically during late July & August anyway – Parliament not sitting, ministers away, & civil servants have families to take on holiday too. For those who remain it tends to be a time for tidying up loose ends, putting things in order, getting ready for the new year, not running around like headless chickens in response to the latest media frenzy.
In any case the rules sound exactly the same as have been in force since the year dot, to cope with ‘serious disruptions’ to public transport – for example the plague of rail strikes in the 1970s & 1980s.
Nobody has mentioned the bit about sleeping overnight in your office on a government-issue camp bed.
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