scaramanga: This might be a stupid question but..
If the transmitter in Fitzherbert is vertical, does that mean I have to rotate my aerial through 90' to pick up the best reception?

YES - Fitzherbert is vertical polarisation, so the UHF aerial does have to be rotated into a position where it's elements are vertical. See this website for a picture of horizontal and vertical polarised aerials. You will get very poor reception if you have the wrong aerial polarisation.

By the way - ignore any information on that website about specific transmitters, it's a British site and those transmitters are too far away for any of us no matter how good an aerial we have! However the basic principles are the same everywhere, and the site has a lot of good information.