Capital Gains Tax when Exercising Share Options

I work for a US company and as part of by package I am given share Options in the company. I am awarded the Options annually, and they vest over a 5 year period. Say I have 10 Options with an exercise price of £100 and a market value of £120. If I exercise these Options (buy and sell on the same day) I receive £200. Is this £200 liable to Capital Gains Tax? Or, since I did not own the shares until today (when I also sold them) is it exempt?

Hi,
You can see guidance here:
Tax and Employee Share Schemes
Thank you