A few observations from person experience of working in small startups, and large companies. Being part of companies that were sold, and being both ends of attempted takeovers, all in comparison to what I've seen in US companies.
1. In terms of sensible investment, what I've seen is that success breeds success - one success creates wealthy individuals with experience that can lead or by part of the next round.
2. UK markets are quite conservative, cautious and by and large dominated by people who don't understand science and technology, compounding the problem. They tend to want to drip feed money rather than go for the big win.
3. Following on from 1 & 2. There is a culture of selling early, rather than building really big, and if you don't have anyone big in the UK to sell to then it goes abroad.
4. UK government appears to welcome, nay have pride in, the acquisition and destruction of some of the UK's biggest companies by opportunists.
5. UK business leaders typically lack global ambition, nay ego/hubris.
6. UK stock market is rather short term, preferring dividends to inward long term investment - the sort of investment typically required to grow.
So what you get is lots of interesting small to medium size companies - often started in concert with the strong UK academic sector, and/or diaspora from previous successes - and very few transitions to global players.
ARM was one of the few - that's why it's so disappointing to see it sold first to Softbank and now possibly NVidia.
The only silver lining is any change is likely to create a diaspora eager for new opportunities - so in the case of ARM - lots of experienced well off engineers ( more able to take a risk ) in one of the worlds best academic centers of excellence.