Hi,
As a UK resident, you are taxable on your worldwide income.
An employee who acquires shares in connection with his or her employment either free, or in return for a payment that is less than the value of the shares at the time of acquisition, will be chargeable to tax under Part 2 or Part 7 ITEPA 2003.
If a tax charge arises on an award of shares, or when shares are acquired on exercise of an option over shares, Part 11 Chapter 4 ITEPA 2003 requires the employer to operate PAYE if the shares are readily convertible assets.
Employee share schemes are classified as tax advantaged or non-tax advantaged. The main difference is that employees do not usually pay Income Tax when they acquire shares under a tax advantaged scheme. You can see further guidance here:
Tax and Employee Share Schemes
Thank you