How to prevent BBC UK from auto-redirecting to the international site

From my understanding, the restriction on video sites such as the BBC is based on the IP address you are connecting from. The only way around this is to connect from a UK IP address using a VPN or similar. If you are leaving a machine at home, you can install OpenVPN or similar. It may cause an increase in latency and a decrease in bandwidth, but you might still be able to watch the video.

The three TV categories 1500, 800 and 500 (kbps) would seem to relate to the different resolutions you can view SD content.

1500 kbps is the required bitrate for fullsize SD (832 x 468) (just shorter than the width of the website) - this is the default size when you navigate to the TV show (assuming your connection can cope). This is also considered "Normal Bandwidth" (option at bottom of screen.)

500 kbps (or rather 480 kbps) is the required bitrate for the smaller (640 x 360) "popout" player. This is also the "Lower Bandwidth" option - selected at the bottom of the screen (which changes what you see in the main player).

I can't currently see where 800 kbps is used. However, I suspect this might be the default if your connection can't cope with the full width 1500 kbps version. I thought iPlayer used to open at a smaller size by default and there was an option to display full width (like there is with YouTube). The 800 might relate to this smaller size. However, for me it opens full width and there is no option to make it smaller (unless I open it in the "popout" player).

You can right-mouse (context menu) on the streaming video to see what "version" you are viewing. From the popup menu you can also "Toggle info console" that shows you more information. eg. "Current Stream Bitrate: 1500 kbps" / "Avg Streaming Bandwidth: 9828 kbps" / "Stream Buffer Length: 75 seconds".