Until yesterday, John Key had taken in his stride the jokes and jibes about his plan for a national cycleway being a looney tunes idea.

But a rare note of irritation could be heard creeping into the Prime Minister's voice when the subject was raised at his weekly post-Cabinet press conference.

The questions centred on the cycleway's potential cost, which regardless of how it is constructed will stretch exponentially beyond the initial $50 million back-of-an-envelope estimate from the Job Summit.

Asked if the project would go ahead "come hell or high water" because it was very much his political baby, Key replied no, saying any Government-initiated project had to stack up on a value-for-money basis. Then he pointedly added: "If you have some flexibility of mind, it's amazing what you can achieve."

What may be achieved in this case may not be quite as awe-inspiring as the concept has been cracked up to be.

The Prime Minister would not go into detail yesterday, saying officials had drawn up a number of options regarding routes and construction and he would have more to say about it later in the week.

However, it is now likely the grand scheme will begin more modestly at a local or regional level with the development of tracks with scenic or special interest value. The separate projects might fall under some national-level umbrella group or agency. But it could be many years before they are connected into a cycleway which ultimately stretches from North Cape to Bluff.

Realistically, that was always likely to be the case, given the limits on the dollar amounts the Government can budget annually for such a scheme.

If the Prime Minister has erred, it has been in being too enthusiastic about the idea of a "national cycleway" when it would be better termed a "cycle network".

The sheer scale of a national cycleway captured the imagination. But the end result was people getting the wrong end of the stick.

What Key's critics should not underestimate is his determination in his role of Minister of Tourism to get some kind of scheme up and running.

The critics may scoff at the concept, which is already being described as "John's Folly" or Key's version of Think Big - a reference to National's white elephant energy projects of the late 1970s and early 1980s.

But make no mistake. Key is deadly serious about this. Something will happen, simply because as the Prime Minister he has the power to make it happen.