In the UK "upper class" is used almost exclusively for aristocrats. No matter how rich you are, unless there is a viable way for you to hold a title (e.g. Earl), you will not be considered upper class.
Middle class is basically anyone who does knowledge work and has aspirations of home ownership.
Your description of "Kids which need to earn their money usually go straight into apprenticeship or university and earn money promptly" would be very likely to be working class kids in the UK i.e. unlikely to be middle class.
In the UK "upper class" is used almost exclusively for aristocrats. No matter how rich you are, unless there is a viable way for you to hold a title (e.g. Earl), you will not be considered upper class.
Middle class is basically anyone who does knowledge work and has aspirations of home ownership.
Your description of "Kids which need to earn their money usually go straight into apprenticeship or university and earn money promptly" would be very likely to be working class kids in the UK i.e. unlikely to be middle class.