My understanding is that the US way of delineating is more universal, i.e. working class = manual labour. The way it was explained to me, the UK delineation has been skewed historically due to the existence of a larger segment at the pinnacle of feudal wealth. These families were assigned the upper class label, leaving those who are merely very rich with the upper middle class label. The middle class label then bumps down to the next rung on the ladder, which can still include well to do people such as doctors etc.
My understanding is that the US way of delineating is more universal, i.e. working class = manual labour. The way it was explained to me, the UK delineation has been skewed historically due to the existence of a larger segment at the pinnacle of feudal wealth. These families were assigned the upper class label, leaving those who are merely very rich with the upper middle class label. The middle class label then bumps down to the next rung on the ladder, which can still include well to do people such as doctors etc.