It is already too late. You should buy when it's low, not when it's high. Wait for the next crash, and then buy, if you want.
Putting it in BTC rather than cigarettes is a sensible strategy because even if BTC goes up in smoke (see what I did there?), at least that smoke didn't end up inside your lungs.
I'm a smoker. I'm quitting. My cig spend will likely go on BTC. Maybe.
I noticed you're based in London, happen to work near Shoreditch? I'm in contact with Dishoom - trying to get them to accept BTC. Another reason to quit, eh? ;)
There is absolutely no guarantee that low stock will rise [2].
[1] http://en.wikipedia.org/wiki/The_Art_of_Thinking_Clearly
[2] http://www.nasdaq.com/investing/5-stock-market-myths.stm
http://www.businessinsider.com.au/isaac-newton-and-the-south...
Still to late to invest?! :P