Currently I'm a US citizen living in the UK on a Maltese (EU) passport. While I have worked full-time for companies here in the UK, I've recently had an offer to do some freelance work for a company also in the UK. This would mean setting up my own company and becoming self-employed. Because of this, what are the taxes that have to be filed with the US government come tax time? I've looked through the IRS' website and it's a bit confusing. I found the form I have to fill out, but does anyone know how much (maybe percentage wise?) I'd have to pay in US taxes for money earned being self-employed in the UK? The extra income from freelancing would be helpful while I'm looking for something else full-time, but not if it's going to be a headache and mean more money paid out come tax season.
You will be filing the exact same form you've been filing until now (I hope...) which is called form 1040. Attached to it, you'll add a "Schedule C" form and "Schedule SE" form.
Keep in mind the potential effect of the tax and totalization treaties the US has with the UK which may affect your filings. I suggest you talk to a licensed EA/CPA who works with expats in the UK and is familiar with all the issues. There are several prominent offices you can find by Googling.