Get your taxes done using TurboTax

Yes, you must report this income on your United States (US) income tax return.  

It should be reported as a sale with no cost, unless you have a record of the item's cost. Here's the path to follow to enter the transaction in TurboTax:

1. Start at FEDERAL TAXES, then select Wages & Income 
2.  You might see "I'll choose what I work on" > Scroll to Investment Income 1099 B, Stocks, Bonds, Mutual Funds, Other 
3.  Answer the question Did you sell any investments?   
4.  Did you get a 1099 B  yes, then select  "I'll type it myself'
5.  Enter the UK-Company Name as bank or brokerage
6.  Enter 1099 B info as Sale #1 with cost data if you have it, otherwise, you can add the fees charged as the cost basis.     

It's quite possible when you get the money the United Kingdom (UK) tax has already been withheld.  If so, you would be entitled to the foreign tax credit (Form 1116).   

• Claiming the Foreign Tax Credit
• Where do I enter the Foreign Tax Credit? 

The letter likely shows the date or you can use the date on the letter.  It would be best to wait for the transfer to see if the UK tax has been withheld, if possible.  You can choose to file an extension or your can file your return and then do an amendment to take advantage of the credit for the taxes paid to the UK. 

I can't be certain of the UK requirements, here is a link for nonresident review: Tax on your UK Income if you live abroad

• Double Taxation Agreement with the US (may receive relief of any UK tax).