Don’t refer to the Office for National Statistics as ONS or the Office for National Statistics when writing. Always use personal pronouns, unless you are referring to the physical building.
Our offices in Newport and Titchfield
The ONS building in Newport has a new lift
Our building in Newport…
The word “the” is not part of the official title but should be included if the term “ONS” is used adjectivally:
the ONS building