On the news this morning they mentioned that Cameron had said he would be nervous at imposing such a ban, so it has at least to some small degree been mentioned in government, perhaps not officially.
I doubt it would have much effect on me either way as I'm a none smoker. Personally I'd like to see smoking banned whilst driving, but more so in public places such as streets. I actually hate people smoking in streets more as it gets in your face and makes you stink. At least in their cars they're just stinking themselves up.