Labour and National are clashing over a potential mega-tunnel underneath Wellington. 

The government's looking at a tunnel connecting The Terrace and Kilbirnie, a distance of around 4km. 

It has been proposed to bring down travel times and reduce congestion on state highways. 

National's Mark Mitchell told Mike Hosking that they're going through a business case and analysis. 

But Labour's Ginny Andersen, based in Lower Hutt, is sceptical about how it'll happen. 

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