For decades research has shown that financial incentives are not as effective as we might think in encouraging people to adopt target behaviours. On the contrary: Overt financial incentive can actually undermine the intended effect, making the very activity it aims to encourage seem less appealing. This phenomenon belongs to an area of study called the psychology of compliance. And rather than bore you with the seminal "wooden pegs" experiment (see: Festinger & Carlsmith, 1954) that spawned this line of research, let me try to illustrate with a real-world example:
Imagine you are in a new restaurant with a friend. The friend orders an unfamiliar-looking dish. On first impression, the dish looks neither good nor bad; you feel more or less neutral toward it. Holding out a spoonful your friend then says: "Here, taste this."
What would be your response?
Now, hold that thought, and imagine that instead your friend says: "Here, taste this. I'll pay you $10."
What would your response be then?
Chances are, that regardless of whether you actually end up eating the food you're offered, the latter scenario is less likely to make you expect it to taste good. If it tasted good, then why would your friend need to coax you with money? What's the catch?
In the best case scenario, if the price is right then offering financial incentive for an activity can result in temporary compliance in a very narrow context (i.e. "sure, for 10 bucks I'll try it"). But when it comes to activities such as transportation cycling - where the goal is to effect (finally, I get to use this word correctly!) long-term change - the technique is ultimately unhelpful, since it will not lead to an internalised preference for the activity.
Coming back to the UK cycle to work scheme, a somewhat related phenomenon is at play. The scheme - offering substantial discounts on the purchase of bicycles - is extremely popular in this corner of Northern Ireland ...which is remarkable, considering how few people actually cycle to work around here. What happens is, bicycle shops (or any big shop selling bicycles, such as Halford's) promote the heck out of the scheme as a means of getting people to buy a new bicycle. And buy a new bicycle they do. After all, who can pass up a 42% off deal? But in my observation, the purchase seldom leads to actually using the bike as intended by the program - that is, to commute to work. At best, the bicycle is used recreationally. But perhaps more commonly, it is used not at all, languishing for a year before it surfaces in the local for-sale ads. Either way, the person who took advantage of the bike to work scheme continues driving to work. So even though this financial incentive "succeeds" in the immediate sense that a new bicycle is purchased, it fails spectacularly in its true purpose: to encouraging two-wheeled commuting.
All of this is not to say that financial incentives cannot ever work. We all constantly make decisions in favour of an activity based on it being more cost-effective. But the key here is, that in order for the financial incentive to be attractive at an intrinsic, commitment-indusing level, we must feel as if we ourselves "discover" it, or at least that we voluntarily arrive at perceiving the choice as more cost-effective or lucrative - rather than being overtly lured with financial incentive by a party with their own agenda. It is an important distinction, and one that ought to be taken into consideration in projects involving financial incentives for cycling.