Kelly, please read the document and its links at the head of this thread - It (and the quote I pasted) is dated 25th March 2009. Your accountant is out of date/misinformed - HMRC website is quite clear.
The old rule was, as you said, neither the day of arrival nor the day of departure counted - This in effect changed to only the day of arrival counting, (though there were fears it would be both following that high court ruling).