That part of the article was just wrong, to be fair (I used to be head of the front-end community at GDS and helped set things like browser support schedules). Our default approach was to add up all browser share (yes, based on GA, but this was a while ago) until we got to 99%, then removed the browsers that were left over. So typically we wouldn’t consider dropping a browser version until it was less than 0.4% usage. You can use a colleague’s client-side tool to test this approach: http://edds.github.io/browser-matrix/ (assuming it still works).

The browser support is currently listed at https://www.gov.uk/service-manual/technology/designing-for-d... . The mention of 2% is specific to IE11, so I guess this was special-cased at some point.