The Lib Dems want to ban all UK petrol and engine cars from 2040. Backed by Lib Dem president Tim Farron, the change in the law could even be brought forward, if electric car and hybrid development tech surges faster than present levels. Their new manifesto also backs more congestion charging and public transport. Are the Lib Dem manifesto promises right, or realistic? %VIRTUAL-SkimlinksPromo%
Paul Watters from the AA doesn't think the Lib Dems are either. "You can't just ban petrol and diesel cases on a particular date," he told AOL Money. "It would need to be an evolution rather than a revolution."
"You can't set a date until you really know the parameters of the technology. If you ask anyone with tech expertise in the industry, they'd say 2040 was premature."
Although some sixties and seventies cars survive now, most have succumbed to the rot. Cars built from hot-dip galvanised steel - the practice increased during the 1990s - stand a better chance. Unless, of course, electric gremlins get there first.
"We're making good strides on reducing CO2 and getting the tech out there, but electric vehicles don't supply the solution except for city dwellers," says Watters. "Will things have moved on sufficiently for the Lib Dems? I'm not sure."
The Lib Dems also want to replace air passenger duty with a per-plane duty, charged in proportion to a journey's carbon emissions; they also oppose any plans for extra runways at Heathrow, Gatwick and Stansted, or for a Thames Estuary airport.
But perhaps the biggest energy commitment change is 2050 - the target date by which all of the UK's electricity is generated from sustainable energy, "setting a target of 50 per cent of electricity generation from renewable sources by 2030 and putting in place a legally binding target for the decarbonisation of the electricity sector."
Lib Dem party president Tim Farron claims if the UK economy "is not green, it will be neither competitive nor successful." Download the manifesto here.
The most economical cars to run
Lib Dems vow to scrap petrol and diesel cars by 2040
Official mpg: 57.6mpg True mpg: 45.4mpg
The third generation Seat Leon is the most economical car to run according to the WhatCar? True mpg test.
It's been a good year for the Spanish manufacturer as the Leon also won the Auto Express New Car Award 2013 after years of missing out to sister brands Volkswagon and Skoda.
The 1.2 TSI 105 has the smallest engine of the top six cars in the WhatCar? lineup, so unsurprisingly is the most efficient of the group.
As well as being efficient it's a great family car. You get plenty of cabin space and an impressive boot size of 380 litres - 65 litres more than in a Ford Focus!
The cheapest in the range is the 1.2 S-trim, but even as a starter model you get a decent standard of equipment with things like air-conditioning, Bluetooth, 5" colour multimedia screen and tyre-pressure monitoring included.
You can buy a new Seat Leon 1.2 TSI 105 S 5-door from £15,850.
Official mpg: 55.4mpg True mpg: 42.8mpg
The stylish Mazda 3 is second on the list of the most economical family cars to run. And like the Seat you can get a starter model relatively cheaply, but with a generous helping of the best mod cons.
The entry-level SE models come with alloy wheels, Bluetooth and air-conditioning as standard. Plus, in terms of size, the 3 is almost on par with the Seat Leon.
WhatCar? says it's a fun car to drive and although it misses out on the top spot for fuel economy, it's not far off so worth a look.
The 2.0 Skyactiv-G 120 5-door is available from £16,995.
Official mpg: 54.3mpg True mpg: 42.5mpg
The Audi A3 was named Car of the Year 2013 by WhatCar?, but only manages third place on its list of the most economical family cars to run.
It's not the cheapest motor, but the A3 offers plenty of space with a boot size of 380 litres on the Sportback. That's perfect for a family with a lot of gear to transport.
WhatCar? says it should definitely make the shortlist if you are looking for a decent sized hatchback.
The Audi A3 Sportback 1.4 TFSI 122 5-door can be purchased from £20,200
Official mpg: 52.3mpg True mpg: 42.1mpg
The Kia Ceed provides an exceptional amount of space (1,318 litres with the seats down) and comfortably transports five adults.
Its large 1.6 engine can almost match the economy of rivals, but WhatCar? says the petrol version of this car is a disappointment compared to the diesel in terms of driver enjoyment.
The Kia Ceed is available in four trim levels. Top level Ceed '4' gets you parallel park assist system (PPAS) which automatically parks your car! But your basic trim '2' isn't exactly rubbish with reverse parking sensors included.
The Kia Ceed '2' 1.6 GDi 133 5-door is available from £16,195 and comes with the Kia seven-year warranty.
Official mpg: 51.4mpg True mpg: 41.5mpg
The new A-Class looks pretty great with its sharp exterior and smart cabin, and the A180 has attracted high praise from the likes of Top Gear magazine who claim it's enough to rival the BMW1-Series and the Audi A3.
But WhatCar? says that even though safety and equipment levels are up there with the best (you get alloy wheels, Bluetooth and air-conditioning as standard with every model) it's a disappointment to drive.
If you want to be the judge, the A180 is the cheapest Benz you can buy. You can get the A180 BlueEfficiency 122 five-door from £20,370.
It's not the most stylish motor of the lineup but WhatCar? reports that the petrol engines are smooth and quiet, while the cabin is a comfortable and spacious place to sit - six-foot adults can sit comfoirtably behind similar-sized adults at the front with leg-room to spare!
If you fancy it the 1.4 TSI 140 is available from £18,390.