TL;DR:

• Inter-disciplinary thought and research is increasingly valuable, and often depends on mathematics.
• UK high school standards are low and declining, especially in math and stats.
• The high variation in school performance even in the same socio-economic group suggests that the problem is teaching quality (and low standards), not money.
• There ought to be action to get rid of bad teachers and bad school managers.
• There ought to be research to find out what the highest realistic standards can be (eg what fraction of students are inherently capable of learning integrals).