> How did TTC get a monopoly in the first place? All of that capital raising and infrastructure building would have been noticed by other people in the economy and attracted competition well before there was 100% market penetration.

In reality when it comes to telecom markets, many of the big ones were granted monopoly rights.  I still believe it could have worked out without government intervention - maybe not at the biggest scales, but still ... if one company would start with telephone lines while everyone else are using horses for message delivery, one can get quite a competitive edge.  It's of course risk taking at its fines level ... one can say that people should be rewarded for taking risks, but it is harmful for the society that one company has such a big grip on the market decades later.

If TCC would be starting i.e. in City of London, expanding to Westminster and so forth ... even if another company starts in another borough of London, the TCC could gain such an upper hand that they could gradually overtake customers from the competitors or buy up the competitors, becoming the de-facto monopolist in all UK.  Fully possible I think ... but it's quite hypothetical.

Microsoft, Facebook and Google are the bigger elephants in the room, internationally.