As you live in the UK and have US stocks, depending on the type of shares you hold, you may need to complete a new W-8BEN form (even if you've already completed one on NetBenefits), which reduces the amount of tax the US government charges you on any income earned from US shares from 30% to 15%. Fidelity, in common with other investment platforms, requires customers dealing in US shares to provide a W-8BEN form within two weeks of the transfer request. It's quick and easy to complete your W-8BEN online and, if required, you’ll be directed to this form once you start the transfer process.
Once you’ve completed the W-8BEN in the Profile section of your account, under 'Preference centre' > 'Investing in US shares (W-8BEN)', the form will be valid for 3 years. You won’t need anything else to trade and hold US shares.