For what it’s worth, for extremely sensitive projects like GOV.UK Verify other options are fine; Verify uses a local Piwik instance.
You’re also welcome to block that specific JS or just turn off JS completely on GOV.UK properties - everything has to work without JS to go live on GOV.UK.[2]
[1] https://support.google.com/analytics/answer/2763052?hl=en
[2] https://www.gov.uk/service-manual/technology/using-progressi...