This will simply legitimise drivers passing too close on faster roads and is contrary to current Highway Code guidance. In any case these No. 10 polls are meaningless unless they get hundreds of thousands of signatures, which this one won't.
I'm not sure about that.
As you not above, the relevant part of the highway code (rule 163) is guidance, not law (i.e. uses "should" language rather than "must").
A "you must allow a minimum of 3 feet" law would set out a minimum standard of overtaking below which action could be taken against a driver. It is stated in unambiguous terms (a distance) that all motorists should be able to understand and interpret correctly (rather than phrased as a comparison with a measure of variable width: "as much space as you would a car" which could, i'm sure be (mis?)-interpreted as less than 3 feet on any case ... how much space do drivers leave on average between their passenger wing mirror and the driver side wing mirror of a car they're overtaking?).
Personally, I'd prefer to see the law changed such that language in rule 163 became "must", but that isn't going to happen any time soon, I think.
I think the proposal in the petition is meant in addition to the current guidance in the HC, and doesn't stop those drives who currently obey that guidance from continuing to do so, but also makes the behaviour of a proportion of those drivers who don't obey the guidance an actionable offence.
I'm not sure I see how that can be counter-productive.
The "three feet" rule would be a bit of a blunt instrument, that really should be refined to take into account road conditions, speeds etc. but sometimes a blunt instrument is better than nothing: if you don't mind picking through the bits afterwards, you
can open a walnut with a sledgehammer.