I find sites like https://mediabiasfactcheck.com/ to be be helpful.
According to them (and similar organizations have similar ratings);
BBC and Sky News: highly factual reporting and centrist (a very marginal left wing bias, but not to the point that they even approach being centre-left)
Channel 4: highly factual but a clear centre-left bias
GB News: somewhat factual with an extreme right wing bias
It’s interesting that, absent GB News, none of the major news channels were found to have a right wing bias at all. BBC and Sky News are essentially centrist but to the extent they have any lean, it’s very slightly to the left.
The print media in the UK is very different and mostly has a right wing bias - I imagine the disconnect between the biased print media and the relatively unbiased BBC and Sky News is part of what causes so many on the right to perceive a strong left wing bias on those stations (and, similarly, those who get their news predominantly from left wing sources like the Guardian to view those centrist networks as having a right wing bias).
It’s a shame that relatively balanced reporting is losing popularity though and it doesn’t bode well for the future of UK politics.
And unfortunately, most of the most biased of the general public, left and right, will label organizations that review media biases as being biased themselves.