Smoking -- follow the money
The simple fact is that smoking is not as profitable for the Government as it used to be.
Back in the days, almost everybody smoked; so tobacco duty was, to all intents and purposes, a general tax.
Nowadays, thanks to the opening-up of internal borders within the EU, only a small proportion of the cigarettes smoked in Britain have actually had any duty paid on them in Britain. Most have been imported from other EU countries, where duty rates are lower but whose healthcare schemes are run on different lines -- often requiring smokers to pay for private medical insurance. Whenever you buy tobacco in, say, Belgium or Spain to avoid the level of duty imposed in Britain, you are not paying duty to the British NHS. Then there are various trans-shipment scams which result in no duty actually being paid anywhere. There is even a market in counterfeit rolling tobacco, packaged up to look like Golden Virginia or Old Holborn, complete with health warnings -- and of course, nobody is paying duty on this!
When you add up the effects on cigarette duty from cheap imported tobacco, subsidised nicotine patches for those seeking to kick the habit and plentiful (i.e. feasible to smoke neat) homegrown marijuana, it's not worth it anymore. Hence the Government seeking to eradicate the smoking habit altogether -- especially when you consider that those who smoke imported tobacco probably won't be looking abroad for treatment when they get cancer. Smokers are costing too much for what they bring in.
Therefore, the Government requires another source of revenue -- and preferably one which will have the least impact on those who have the most money (therefore, definitely *not* an income-dependent tax) -- ideally, a tax on something people have no choice but to do and therefore have no choice but to pay it.
The motor car has already -- for all practical purposes -- successfully been reclassified from "luxury" to "necessity", so as to create another effective general tax. The harsh reality, to which MPs in London are oblivious, is that many people have no choice but to use their cars. A decent, integrated public transport system would reduce car use and therefore government revenue, so isn't going to happen. London is a special case: for one thing, the capital's roads would seize solid if everyone riding the buses and tubes was forced into cars; and for another, many tourists coming to the UK *only* visit London, thus receiving a skewed impression of the general state of public transport in the UK.
But the real "holy grail" would be a tax on food. So far, the public has been unequivocal in its opposition to such a thing. Hence the demonisation of "obesity", with examples being trotted out on a daily basis to convince the British public to accept the notion of a food tax. (As a useful aside, a specific campaign against *childhood* obesity can be exploited to get kids used to the idea of having The Authorities probe into their lives from an early age: school lunchbox inspections and so forth are an ideal way to acclimatise them to heavy state intervention. It is a small step from telling someone what to eat to telling them what to think.) Initially, of course, the food tax will just cover chocolate, chips and salt; but history shows that the scope of taxes is never narrowed. Potatoes will be taxed, under the colour that they could be made into chips; and so forth. Eventually, it won't be possible to buy an organic rocket salad with fat-free, vinegar-free, egg-free, dairy-free, salt-free, taste-free dressing without paying tax on it.