NOt sure about the polarity, but you can tell by hooking it up before connecting it. I have never had any problems with polarity in US cars.
Most likely, you have an LCM that can't be programmed. On earlier E46s, you can just pull a fuse. Can't remember which one it is for sure. You can pull #32 and see what happens.
Not sure about the laws in UK, but they should be DS2s. Check the lights to make sure.