At the risk of bringing Brexit into this discussion, there is a reason why turnout was so high in the DE sociodemographic. More than one generation of British youngsters have been let down because it was easier to employ from abroad. When we opened up the jobs market to Eastern Europe, there were people coming over who were completely overqualified for the jobs they applied for and got. An 18 year old straight out of college with no experience or a 25 year old qualified accountant, for example, willing to start at the bottom to get a toehold in the country.
There was a hotel I visited every year in Oxfordshire that basically ran on 16-18 year old kids from the village working there in holidays and weekends. It was quintessentially English with really lovely, well turned out, eloquent youngsters adding to the vibe. Within 5 years, the whole place was Polish. This has happened up and down the country. Kids can't get experience in anything.
Whatever the rights and wrongs of Brexit, allowing freedom of movement between countries with such disparate economies has been a disaster. This plan sounds as though Labour are at least aware that not investing in British youngsters is no longer an option.