Short Term Strategies -- From http://www.forbes.com/2008/03/06/solutions-green-car-kolodziej-oped-cx_rko_0307kolodziej.html?partner=alerts. 

“What to do? One increasingly attractive option is to power vehicles with natural gas. Natural gas is plentiful, cleaner and far less expensive. Depending on the region of the country, natural gas is 75 cents to $2 less than the diesel-gallon equivalent (i.e., for the same amount of energy in a gallon of diesel fuel) at the pump. For truckers buying 15,000 gallons of diesel per year, that's $11,000 to $30,000 in annual savings. Additionally, since 85% of the natural gas used in the U.S. is produced here, with another 12% produced in Canada, natural gas vehicles reduce our dependence on foreign oil.”

Introductory notes:

The wholesale price of gas deliverable today quadrupled to as much as 255 pence a therm due to supply fears.

US Gallon to Litres:        4 to 15.1416472

UK Gallon to Litres:        4 to 18.18436

US$ to GBP: 1 U.S. dollar = 0.496672296 British pounds

US¢ to GP Penny: 1¢  = 0.496672296 GP pence

UK Gallon to US Gallon = 1.2

Translation to March 2008, UK: “What to do? One increasingly attractive option is to power vehicles with natural gas. Natural gas is plentiful, cleaner and far less expensive. Depending on the region of the country, natural gas is 75 cents (32.04 pence) to $2 (£0.828) less than the diesel-gallon equivalent (i.e., for the same amount of energy in a gallon of diesel fuel) at the pump. For truckers buying 12,500 gallons of diesel per year, that's $11,000 (£9167) to $30,000 (£14,500) in annual savings.”

This seems to make no significant difference in emissions of CO2, and the main difference in cost is because of tax, a matter easily changed by the government at its sole discretion.  Probably the cheapest way to produce hydrogen for use as fuel, instead of electrolyzing water, is to get it from natural gas.  If this can be done cheaper and without leaving the residues of carbon (as CO2, or CO) or methane in the atmosphere, perhaps that is one possible option