Starter for Ten
Nominet is just the first of n - where n+1 might be nearer the number of targets.
Nominet should and probably has one of the strongest security layered system structure of any company. Compromising a Domain Registry is getting close to a zero day for the internet (or at least the UK section of it).
Reading between the lines of Nominet's letter and touching wood - those layers appear to have held and the threat detected - and presumably reported back to the vendor rather than the other way round. Others may not be so lucky - yet only one public report to the NCSC? If you are using the product the NCSC protocols pretty much make that mandatory if the exploiter could access production system through possible compromised credentials or similar.