A lot of these industries are national enterprises in other countries, including in the EU. Indeed much of our private transport infrastructure - trains, buses - are run by the state owned companies of Germany, Italy, and France.
There's no issue of legality, once franchises expire, they can be returned to the state - see North Eastern rail. Publicly listed companies can be bought by anyone.
I often wonder, when talking to Conservatives, both UK and US, what they think the functional difference is between paying Tax for these services, for no profit, or paying rent to private companies where 30%+ is gone to the shareholders, and the company even then is held up by government grants and funding from taxes to pay for investment and maintenance of infrastructure. That private layer seems entirely superfluous.
The idea of having a choice between who to pay that rent to, to line their pockets, is just an unnecessary extra burden - just as it is in healthcare.
It's very obviously a means of passing taxpayer expenditure around to allow private individuals and corporations to take a cut of those taxes. It's a massive scam.
I have no idea what went on in the 60s - 70s, but the sellout of national assets when Thatcher was put in charge of it made a lot of rich people richer, and poor people a lot more plentiful; and left us with a nation progressively stripped of the assets it needs to exist as a nation.