I recently undertook some work for a US company. To have them pay me, I needed to get an ITIN number, which meant visiting the US embassy in Grosvenor Square.
From the documentation, I understand that I had to do this because of a tax treaty between the US and UK to stop people working for overseas companies and not declaring it. I presume that the US Internal Revenue Service informs the UK tax man of what I'm up to, and my ITIN is linked to my NI number.
My question is perhaps obvious: does the UK tax man ever get to hear about how much money I make with the US company? Or is he merely made aware that I am now working for the US company in some capacity?