Free Left Turn

They have them in America, they have them in India and presumably various other places too. Japan has a combination of a free left turn coupled with a priority crossing for pedestrians so that traffic is never blocked by people who aren't actually crossing. For some reason in the UK it has never happened.
Picture this, Cheltenham Ring Road, dual carriageway, rush hour in the morning so really busy. A car is leaving a side road, just one car, and he is turning left onto the dual carriageway. Common sense would say, let him wait for a gap and turn left but since we cannot work out anything so complicated, since there are lights to help these same people turn right across traffic, instead all 100 of us had to stop at a red light to let one person out, the total time to change back to green is not soon enough to avoid stopping at the lights and the jokers in councils up and down the country simply insist that these lights help "control" the traffic. Of course they control traffic, they just don't help it at all.
Most lights have detectors in the roads and for various reasons you might want to disallow the free left turn at some junctions but just like part-time signals, why can't this be the default permission for road users and prevent it only where required. Like the US, if you hit someone when turning at a red light, it is always your fault. I fear another idea way beyond what anyone in this country is allowed to do.