> (2) local date-time with a geographical time zone.

Note that timezones aren't just geographical. In London, you'll be in timezone GMT (+0000) for half the year and timezone BST (+0100) for half the year.

If you think instead that you're in a single timezone, then you need to know that your "timezone" isn't linear, it contained 00:00->01:00 twice on 25th October 2009 this year (when the clocks go back).

So "what was the UTC time for 00:30 on 25th October 2009 in London" isn't a question with a well-defined (or unique) answer.