Arethuza, I'm a bit confused by this comment. PhDs in the UK don't last over 4 years. Would you mind clarifying?
From a personal perspective I don't regret my PhD, though it was charity funded so it was topped up to be around £20 000 instead of the usual £14000ish per year. It was an opportunity to engage with a small group of experts in research that was engaging and of use to the wider world, and present it internationally. I also tried to start a start-up during this time, but the underlying idea failed to pass preliminary trials (I work in healthcare). So the two are not mutually exclusive.
People's experience tends to vary. I think a lot depends on how much you research the group and supervisors you will be working with beforehand, and how much you engage them in the research you do.