So what is an ISP? Well, it's like an electricity "supplier" in the UK (eg Bulb passim): it's a thin shell company that buys in a wholesale market and sells to the retail one, while running a call centre to deal with the annoying retail customers. Some people have called this the "playing at shops" theory of market operation.
The UK has leaned more towards the pretend visible competition and underinvestment behind the scenes while allowing profiteering, but even within that there's some room for innovation.
Really boring improvements like saving money on admin by getting customers to pay via Direct Debit or using the internet for customer service were often pioneered by small companies which then forced others to follow to compete. Could a well run nationalised company have done that too. Yes, but they'd have been sabotaged and attacked for political reasons, so in reality its possibly an okay compromise.
Bulb is a good example. Good customer service, non predatory pricing, supporting renewables. Broken by weirdly anti-market moves from a conservative government to patch up other anti-market decisions they'd made to subsidize fossil fuels.
The may be the perception because stats show otherwise: https://en.m.wikipedia.org/wiki/List_of_countries_by_Interne...
The Uk is doing pretty bad.
Switching companies is really easy. You just contact the ISP you want to switch to, and they pretty much sort out everything from there. Prices across the market are pretty similar although there is some non-price competition going on. For example, Sky (the UK provider of satellite TV) will give you a discount if you subscribe to their satellite service making your internet cheaper than it otherwise would've been. In the UK there is the concept of the 'loyalty penalty', a term not only used in regard to the ISP industry but also other services like gas, and electric. It is used to describe the situation where people who stick to one provider tend to be paying higher prices than those who frequently switch providers, and hunt for better deals therefore people are often encouraged to take advantage of how easy switching is.
I hear these stories from the US where people find they only have one provider in their region which is a completely foreign concept to myself. And when I was in British Columbia where some of my family reside, I noticed there seemed to be a duopoly on the ISP market: Shaw, and Telus. They also remarked on how expensive their service was. I don't know what the comparison is but it doesn't surprise me at all under such a market.