The likes of the CEGB and NCB also managed key suppliers to ensure that they had more than one source of critical plant and technology.
The nationalised electricity boards also built a one of the best and most reliable electricity systems in the world.
Unfortunately that system has now been driven into the ground over the last 30 years and is coming to pieces at the seams.
Also as to claims that nationalised utilities have terrible customer service and were slow to respond to requests for service alterations, it's still like that now!
I was waiting months to have my electricity and gas meters moved by a few feet, and months more than that to get a lead replacement water supply installed.
EDIT:
Some people might fantasise that the apparent improvements in the standard of living in the post-Thatcher era have been brought about by the "efficiency" of privatisation, but overwhelmingly tehy are the result of the march of technology, or they are the result of eating the accumulated seedcorn of generations.
We now live in the world the meerkat has wrought - an energy system that is falling apart and is essentially unable to provide reasonably priced energy, a technologically stagnant railway that consumes huge subsidise every year, a telecoms system that can best be described as an utter mess, and airports that fall over at the slightest hiccough, the list goes on. And a collosal and ever increasing budget deficit, largely directed towards subsidising the living standards of the people who voted for this madness in the first place!
What wonders Maggie-worship has brought us.