The mistake Thatcher made was to open up the telecoms market to competition at a time when the legacy provider (BT) were starting to build a high speed internet highway/backbone. In hindsight, this could indeed be considered an error but looking how BT have fared since, perhaps not?

We're now in the absurd situation where 4 out of 6 power generating companies are foreign owned and the Japanese own our chip manufacturer.

All because of her policies that originally envisioned that the share holding would be by the British public, not foreigners.

And the latest scandal is that our water companies are dumping ridiculous amounts of sewage into our waterways while giving out huge dividends. And there's nothing anyone seems to be able to do about it.

I recall Blair saying he regretted not doing enough about energy security when he was in power, I don't recall him blaming Thatcher?

Brown expands nuclear ambitions (2008): The prime minister said that with oil prices soaring, it was time to be "more ambitious" for nuclear plans... http://news.bbc.co.uk/1/hi/uk_politics/7424158.stm

There has been a long history of failure, by both sides of the political spectrum.

Blair was the only other recent politician with similar power. He was actually a fan of privatisation and deregulation (and still is, if you read recent interviews).

And recent governments don't even want to fix it, the status quo benefits their rich donors, even if it's massively hurting Britain's long-term prosperity. You've also got a significant section of the Tory party that still believe in the thoroughly discredited neoliberalism Thatcher followed, as seen by Liz Truss' disastrous tenure.

I'm not a Thatcher hater, but there were a lot of negatives as well as positives.

This is the most charitable interpretation of events (no sarcasm intended[1]), and one I would like to believe, but greed is very powerful and leads people to evil, so I can well imagine various lobbying groups would have seen the easy mid-term money to be made from such sales.

[1] "Never attribute to malice that which may be adequately be explained by incompetence."

She decided it was better to open the market to foreign cable TV providers and so barred BT from selling TV access.

Without TV there was no driver for fibre investment.

Where BT would have had a requirement to provide universal access to fibre, as with phone provision, Telewest and NTL just did geograhically limited roll outs of legacy coax and the rest is history.

Also it denies agency to those in power in the decades that followed. I mean did that decision bind the policymakers that followed when it became clear how important the internet really was?

This seems unbelievable now, but the relevant reference is https://www.techradar.com/news/world-of-tech/how-the-uk-lost...