So my wife thinks the smell was plasticky* and not 100% if the smell and the problem where totally related as she was near an industrial estate that tends to pong regardless. Have disconnected the battery so time will tell if this is an easy fix. The exhaust could possibly be a culprit as it is the stock Nissan jobby and it has truthfully always looked to need replacing as it certainly is showing its patina of 15 years running down the beaches and bush. Don't like my chances of getting the bolts undone below the headers as they look pretty well rusted shut so might have to tackle this tomorrow and see how we go. Hopefully I will get a chance to check for air leaks/vacuum leaks tomorrow too. Let you know how I travel.