I am not saying nor do I think it wise to even "try" and win a conflict or a war or anything of the sort. (we certainly should not try and occupy the country)
All I would want is that we knock out Iran's nuclear bomb making capacity.
As for your point about the UK, Japan, and/or India not supporting us -- I think they would change rapidly if faced with the REAL possibility of a nuclear bomb making factory up and running by the Iranian government, especially a government which is likely harboring many of the top Al-qaeda leaders of today.
I think they'll look at their economies suffering if Iran cuts off oil, and reach an accommodation with the regime in Tehran.