This is the same for both gas and electricity (both import and export for those who can) in the UK.
It generally works quite well, and could be pretty competitive if you knew to shop around. Since Vlad's 3 days began and natural gas prices spiked the entire market (the companies that survived) has pretty much been at the government price cap. There are some deals starting to re-appear but the main reason to switch right now is customer service. Amazing how much brand loyalty let's the big firms treat people like shit and get away with it.

The best deals tend to be time of use for people with smart meters.