Już wiem jaka jest różnica. :)
'the tax office' is a very informal way of referring to a governament office/department concerned with collecting taxes. It could be referring to the tax office of any country.
The Inland Revenue was the offical name for the governmental department responsible for collecting taxes in the UK. A few other countries may also use this name but many countries have completely different names for it. For example, the US calls it the Internal Revenue Service (IRS).
In the UK, in 2005, the Inland Revenue merged with HM Customs and Excise department and there is now a single department called HMRC (Her Majesties Revenue and Customs).