I claimed US-UK tax treaty for my previous visit to US. During that visit, I worked on H1B from September 11, 2009 to June 28, 2010. Then I left US because expiry of visa and worked in China until January 2011. I re-entered US on a H1B visa in January 2011 and do the same type of work as last visit. My questions are:

1. If this visit does NOT extend the time limit terms of the US-UK treaty I claimed during last visit, can I still benefit from the treaty?

2. If this visit extends the time limit terms of the US-UK treaty I claimed during last visit, will IRS tax me for the entire period of last visit ?

3. Since there is an interruption of my US residency in tax year 2010, am I a nonresident alien or resident alien or in dual status when filing tax return for tax year 2010? Will IRS tax me on my China source income?

Did you get W-2 in 2009 and 2010? Who paid you during your stay in US?
H1-B is work visa and you must pay taxes like US residents and citizens.
What tax treaty benefit did you claim?

This is form IRS publication 901.
Income that residents of the United Kingdom receive for services performed in the United States as employees (dependent personal services) is exempt from U.S. income tax if the residents meet the following requirements.
They are in the United States for no more than 183 days in any 12-month period beginning or ending in the tax year.
Their income is paid by, or on behalf of, an employer who is not a U.S. resident.
Their income is not borne by a permanent establishment that the employer has in the United States.

Hi MukatA,

I got W-2 in 2009 and 2010. I work as postdoc fellow in universities during the two separate visits. I claimed US/UK tax treaty during first visit. What I am concerned is the impact of the previous US/UK tax treaty on my this visit since the treaty contains a Retroactive Clause.

What or which treaty benefit did you claim? H1-B do not get any treaty benefit as you were paid by US employer.

According to US-UK tax treaty Article 20 (see the link below)

http://www.irs.gov/pub/irs-trty/uk.pdf

I exempt from US income tax for two years if I conduct research in a US university.

You were not invited for teaching or research. Check your visa stamp. H1-B is work visa. You owe taxes for all the years you worked in U.S.
Did you file your 2009 tax return?

Those invited to teach or do research get J1 visa.