Sorry to be techie but:
mjr@bletchley:~$ host
www.nhs.uk
www.nhs.uk is an alias for nhswebsite-production.edgekey.net.
nhswebsite-production.edgekey.net is an alias for e10931.ig15.akamaiedge.net.
e10931.ig15.akamaiedge.net has address 104.89.75.74
Akamai Edge is a similar sort of thing. Once that's involved (and if it's set up right), you've often no way of telling how many servers are really involved or where. Imagine a website equivalent of Legion from Red Dwarf.
https://en.wikipedia.org/wiki/Akamai_Technologies#Akamai_Intelligent_Edge_Platform https://en.wikipedia.org/wiki/Legion_(Red_Dwarf)
As others mention, their spaceless NHS numbers were accepted... but I believe you and think such neatening might have been removed during a surge.