EMI Tax Exempt - Transfer from UK to US entity

[DavidZ]

hope someone will be able to help.

When joined the company 3.5 years ago, I was issued employee stock options. Recently the company has been acquired by a publicly traded company and employees were able to exercise their vested stocks. Since parent organization is now publicly trading company, I can exercise my stocks and benefit from tax relief.

I am being transferred from the UK company to the US about a week before the trading window opens and can't sell my stocks while employed by the UK entity. Does it mean that if I sell my stocks 10 days later and already be employed by the US entity, I will have to pay US capital gain tax and will lose EMI tax relief?