A lot of what's on HMRC's own site is, sadly, stale or poorly dated.
Yes. And it used to be 10% with no limit until 2008. Those were the days.
Also it's not just the "first time you sell a company". It applies on as many company sales as you want, up to a lifetime total of £10m.
And not even company sales, as far as I understand it, but any group of complete business assets (that is, any set of business assets that defines a single "business" - an important point for sole traders like me ;-))