I don’t believe them for a second. Politicians perpetually tell you one thing, when they mean another. What they are implementing may well be the exact right thing to do, but because they are steered by think-tanks, focus groups and PR arseholes, they feel compelled to spin illogical drivel, when the truth should already be more than enough.
This may well be apocryphal; the “boiling a frog” allegory holds that if you place a frog into a pot of cold water and gradually increase the temperature, the said amphibian will remain blissfully oblivious, until it’s too late. 
Back to the politicians: They frequently tell us that they are seeking to moderate, and change the behaviour of the populace, by means of targeted taxing of carefully selected goods; namely tobacco, alcohol and fuel (gasoline).  As everyone knows, these goods have special taxes levied, which hugely inflate the cost to the consumer, way beyond the charge made by their respective manufacturers.  In the case of fuel, over 65% of the £1.40 per litre price I spent earlier today, goes directly to the government.  In fact, despite being currently frozen, we actually have a tax device called the fuel price accelerator in the UK, which is designed to grow the price at the pump by a rate beyond that of ordinary inflation.   All the while, politicians claim to be saving the planet, by forcing us to consume less fuel. Combined with the price per barrel growth, this makes for a painful experience at the forecourt.  We’re consuming just as much, but paying much more for the privilege.
Not, however, painful enough that people stop driving altogether.  By raising the price in penny increments, the consume gets annoyed, but not enough to sell the car, and take to public transport.  How many people have threatened to do just that when a price hits say £1, £1.20 or £1.30, only to grudgingly succumb when it creeps up by another penny?  The same thing happens with cigarettes.  If the authorities really wanted my dad to stop smoking in the 70’s, they’d have raised the price from 40p to £1 per pack in one move, thereby saving millions from a certain death (and really pissing them off too).
Look, if our elected leaders really want to stop us smoking, drinking and driving (not at the same time), then by all means double the price. But, if they really only want to collect more taxes from those too dependent on these products, then simply carry on as usual.  Only, please be a bit more honest about it.
PS. I think it’s deliberate obfuscation to sell fuel by the litre, when we calculate efficiency in miles per gallon.