UK Civil Partnership: Do I still file as single/unmarried?

So I'm in a Civil Partnership here in UK and I saw a question in another thread asking if they should file as single/unmarried when she/he has since married in UK. The answer was to file as married.

How about civil partnerships? If US doesn't recognise this union/institution then I am still considered single, therefore must file as single/unmarried?

Also, can I use my last paycheck stub in lieu of a W2 Form? Just curious, I heard somewhere you can do that.

The answer is yes to both questions. You file as single if you do not have marriage certificate issued by the state official in any country.
Generally speaking, you can use your last pay stub showing wages for 12 months and taxes paid through the year. That would be acceptable if this document  covered the period from January through December. If your last paystub shows the total for 12 month ending in April, then one paystub is not enough to demonstrate your calendar year earnings. I answered the question about acceptable forms of W2 substitute here: http://talk.uk-yankee.com/index.php?topic=67432.msg945519#msg945519

While you can indeed use payslips - indeed most people do - pleaee take care if the pay is adjusted for pension contributions or salary sacrifice arrangements as the year to date figures for UK tax purposes may be different from the gross amounts taxable under US rules.

As taxesforexpats says, I suspect you already knew that a UK civil partnership is not recognised in any State in the Union - indeed it is sadly and annoyingly only of limited value in the EU outside of the UK.

Thanks for clearing that up, I figured as much anyway about the civil partnerships. I wish more people knew how unequal CPs are to being officially married.

Regarding paycheck stubs. I was just inquiring about using my U.S. paycheck stubs. While I have finally found a job here recently, I'm still waiting on my crb.

Regarding paycheck stubs. I was just inquiring about using my U.S. paycheck stubs.

It's so funny all that discussion was around UK pay stubs while you meant the U.S. document.  I would not recommend doing that because the IRS is very peculiar about the smallest discrepancy when it comes to cross-examination of numbers on your return against officially reported numbers. W2 is officially reported; last pay stub is not and these two documents may be not identical.

If you cannot get form W2, you should attach Form 4852 to your return, Substitute for Form W-2, Wage and Tax Statement. Using last pay stub is not prohibited but you will put yourself at risk of the follow up inquiries and close verification of every number you entered on your tax return.