http://www.statistics.gov.uk/StatBase/ssdataset.asp?vlnk=7280
There is a spreadsheet of where end user UK carbon emissions come from, the only ones rising are transport and "other" although I am sure a lot of the emissions are from commercial as well as domestic.
The scary part is that on current trends, transport could be the largest single contributor of UK CO2 in a few years time.
However, you cannot just Tax this without providing a more viable alternative, and if the Govt want people to use their cars less, they need to provide decent public transport links. If everyone who could use public transport all did so, on the same day, chaos would be the outcome.
I would like to see more rail freight terminals used, reduce commercial vehicle miles, 1 train from London to Scotland (or any other major route) is way better than 40 container lorries.
The roads would also become safer with less commercial vehicles (not due to the commercial vehicle drivers themselves, but due to the way many people drive when stuck behind a commercial vehicle for any distance).
I Don't agree with taxing a problem to make it go away, it doesnt work, it punishes those who have no alternative, what we need is investment in infrastructure to increase the viability of alternatives. Only with a viable comfortable alternative will people give up their cars for their daily commute.
Electric cars has been tried before, it was quite successful in California before Bush and his team (inc Arnie) destroyed them in favour of the mythical Hydrogen Fuel Cell, a technology that actually nets more CO2 emissions than fossil fuel.
I can recommend "Who Killed the Electric Car" as compulsive viewing, and battery technology has moved on a lot since then!