When Harold Wilson was Prime Minister, the top rate of income tax was 83 per cent.But it could be as high as 98 per cent because the government imposed an extra levy of 15 per cent on 'unearned income', meaning investment and dividend income. That was in 1974. The top rate was for income over £20,000, roughly £155, 000 now.
The result was a) that people left the country, to become tax exiles, or just took employment abroad. It was income that was targetted, and therefore moving the generator of that income, the taxpayer, was not very difficult.
b) people took advantage of company law, to get companies they controlled or were directors of to supply them with what they would otherwise have paid for out of income. With care taken, these benefits escaped being classified as income.
c) they relied on capital gains. Throughout the Labour governments of the 60s and 70s, capital gains were not heavily taxed. At one time, as I recall, capital gains were tax free unless the gain was made within 6 months of the acquisition. That measure was introduced to stop speculators (!)
There were, in consequence, a great number of people whose declared income, though quite large for the time, mysteriously fell just short of the highest rate bands, when it had been well within them before.
Did it work and bring benefits to the country? No. But it made the Left happy and pleased accountants and tax advisers.