For every £2 that your adjusted net income exceeds £100,000, the £11,850 personal allowance is reduced by £1. Pension contributions and Gift Aid can help to reduce adjusted net income and save tax at an effective rate of 60%.
The restriction applies between £100,000 and £123,700 adjusted net income. Another way that you could avoid this trap would be to agree with your employer to sacrifice some of your salary in exchange for a tax-free benefit in kind. These rules changed from 6 April 2017 but employer pension contributions, bicycles, and employer-provided childcare would continue to be tax effective.