If you are employed, your employer's payroll department should be able to tell you, and provide you with a tax office reference number (which will be your employer's tax referenc).
It doesn't matter where you live - it's where your employer's head office is that counts. Even then there are some oddities - all civil servants have their tax office in Cardiff for example.
if you look on your pay slip should have tax reference number that is the office so if you ring any tax office and give them that reference and your national insurance number they can track you - it goes by your employer as to where it is based