If I'm remembering correctly, it's because the previous government set the price floor to the average natural gas price, artificially propping up their north sea oil & gas industry that's been noncompetitive for decades. Even though they can make cheap energy, consumers get screwed because of national security concerns.

Unfortunately I don't have a source, and would appreciate a UK national with better understanding than me to chime in :)

That has two causes, dependency on natural gas, which would be worse without renewables and taxes, which is unrelated to renewables and related to general policy goals of reducing energy demand.

Also even in a European context UK power prices aren’t as high as many of its peers.

Germany is even more expensive.