"But the trend over the last 50 years is to privatise even schools, so I can't see it happening."
Well, look at the standard of state schooling. In too many areas it's absolutely atrocious. With some experience of both I'd say that at their best the state schools are easily as good as independent schools, unfortunately that means that the other 95% of state schools are worse for no good reason, despite a near monopoly and "democratic" control by local authorities. The arguments about funding for state schools being worse don't hold water (a) because the state can decide what it wants to pay for education, and (b) the best state schools don't generally get preferential funding over the cr@p ones (if anything the reverse).
Now look at water. When state managed it was vastly over-manned, drinking water quality was low, and wastewater quality even worse. Investment was routinely curtailed (by the treasury) leading to a collection of ineffective and obsolete assets, even as the government signed up to agressive EU targets on water quality.
If the state penny pinches on example matters of water and education, why do you think for one moment that it would be competent steward of telecoms infrastructure? Last time it was state controlled it took forever to get a basic fixed line installed, you often had to share a line with neighbours due to under-investment, and you got a crummy bakelite phone that looked like something from the 1940s (because it was). If you passed the mobile infrastructure to government, they'd need to stump up many billions of additonal government debt (unless you know where an equivalent amount of cash is being wasted), and government would be even less inclined to invest in not-spots than the commercial operators. Next year the treasury would be looking to try and reduce the huge public borrowing costs, so investment would be slashed, and prices would go up because that would be income for the Treasury.
I'm staggered that you could believe that government would be a good steward of any asset. They have proven themselves utterly incompetent in fiscal policy, trade & industrial policy, energy policy, foreign policy, industrial policy, education, welfare, technology policy, and in all aspects of infrastructure planning, and still you think that they will be better than commercial operators at owning and operating anything?