I imagine most people will have seen this already but UKFI has set out its stall in a framework doument published on Monday and which is now available on the website. My own area of geeky interest - how it deals with the 'ownership' side of things - is explained in a section on page 9 of the doc. It says that UKFI will intervene in there are concerns about strategy, performance or acquisitions (!) or disposals. It also says that UKFI will vote its shares, tell the investee companies in advance how it will vote its shares, and disclose how it has voted. It will also report ton HMT on the effectiveness of its engagement. The doc also talks about consulting with other shareholders where necesssary.
There's more detail in the appendix, which I'll probably post a bit more about when back at work.