You are not a resident of the UK unless you intend to stay there permanently, or return to the UK after being away.
What makes you a resident of
a state (or country)?
Generally, you're
a resident of a state (or country) if you intend to either stay there
permanently, or return there after a temporary absence. It's where
home is – where you come back to after being away on vacation, business trip,
overseas employment, or school. Many factors are considered, not the least
of which are where you are registered to vote, own homestead property and are
licensed to drive.
Even if you were a resident of the UK, as a U.S. citizen you would still be subject to U.S. tax laws, including the requirement to report foreign bank accounts.
You would use Form 8938 to report your
specified foreign financial assets, but only if the
total value of all the specified foreign
financial assets in which you have an
interest is more than the appropriate
reporting threshold.
If you are
not married, the reporting
threshold of your
specified foreign financial assets is "more than $50,000 on the last day of
the tax year or more than $75,000 at
any time during the tax year."
For more information, see: https://www.irs.gov/pub/irs-pdf/i8938.pdf
