Having recently done some work for one our clients on this, I thought it maybe useful to share this with you all.
The bit of earnings between £100,000 and £114,950 is one of the most highly taxed bits of income you have. Not only do you pay 40% tax on it, but for every £2 earned over £100,000 you also lose £1 of your personal allowance (to £7,475). Therefore if you earn £114,950 or above, your personal allowance will be completely lost.