I think the issue is the proportion of people who contribute the most tax is decreasing rapidly.
Last year alone, London lost 11,300 dollar millionaires (only surpassed by Moscow)
The top 1% pay 30% of all tax
The top 0.01% (4000 people) pay 6% of all tax (£17.billion/year or £4 million each)
If one leaves, we need 1,300 average tax payers to fill the hole.
The main reason is the retrospective nature of RRs trust reforms. This affects non doms who are fleeing as the UK is seen as anti wealth. RR assumed these reforms would raise money. In fact, it is likely to cost us billions and those tax payers are unlikely go come back.
Well done Labour. Idealogical fiddling while Rome burns (although it doesn't, because all the millionaires are relocating there!)