UK Advisor providing services to US startup but rewarded in shares

I have an opportunity to provide Advice to the Board of a US startup company in return for either shares or share options, which would vest monthly over a 2 year period. I am a UK tax resident and would be providing the advisory services remotely from my office in the UK. The advisory services would be incremental to my primary means of employment here in the UK. I am not currently set up as a limited company or freelancer so can be flexible on the most suitable approach. The startup is in very early stages, but there are planned investment milestones over the 2 year vesting period that could potentially increase the value of the shares, though it is unlikely there would be an opportunity to trade them within that 2 year period. If I go for Restricted Shares to myself as an individual I am concerned that I may incur tax at the point shares vest - and therefore incur an unaffordable cashflow issue as I wouldn't get any cash value from them until they are sold? Is my assumption correct? However, I am considering setting up a Personal Service Company (with the primary reason of helping limit my personal legal liability of dealing with a US company). In which case the Advisor agreement would be made in the name of my Personal Service Company. In this case am I then correct in assuming that tax would not be due until the shares are exercised? Or would they still be deemed as being to myself as an individual as they are for my advisory services under my own personal service company?

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Hi
Income tax is payable on the shares when they vest.  The company may deduct the tax by withholding shares to cover the tax.  You may have to claim a foreign tax credit in your self assessment tax return,  for tax paid in the USA.
If the shares are disposed of immediately, there is no capital gains aspect.  If you retain the shares and dispose of at a later date, then capital gains rules come into effect.

Thanks for the reply. In this example the advisor is treated as an independent contractor by the US startup company, so tax would not be withheld to cover tax in the US, the responsibility is on the Advisor for tax/legal obligations. Also the startup company is early stage and unlisted so would not be feasible to dispose of them immediately. 1) Does this alter your response? Plus, On the UK side of things: 2) Is a Section 431 Election applicable? Operationally Advisory Board members are not Non Executive directors, nor employees, but would a board advisor be seen as a Non Executive Director for HMRC purposes? 3) At the point shares vest - Would the fair market value of shares determined in the US still be applicable, or would an independent valuation be needed in the UK? Thanks in advance

Hi,
1. NO
2. As  you have not actually set up a company as yet, then the S431 is not applicable, if you do then this would be financial advise which we are not authorised to give. advisary board members are not directors  
3. We would accept the market value.
Thank you.