The UK bluray is region free. It has most of the extras but they removed the isolated music and sound effects track and the AC3 5.1 audio track. It does have the original stereo mix and the running commentary tracks in LPCM, though. I'm considering making my own custom bluray that has the 1080p video and all of the audio options of both versions.
Yes, the UK Second Sight release has 1080p video. It also uses the same 480i NTSC video files as the US release for the extras. No Pal speedup or frame blending mess.