.You say you are "keen to get the extra power and fuel economy without physically changing anything on the car at all"....Extra power and fuel economy are not two features that sit comfortably together. Without changing hardware such as to a high flow exhaust and air intake, a remap is not going to deliver you significant extra power.As for not declaring any mods to your insurer, you would be taking a big risk. You cannot possibly predict what kind of accident you might be involved in and if someone is seriously injured your car may be impounded and very closely inspected. Contrary to what some tuners may claim, there are specialist experts who can tell even if your car is rendered undriveable. I'm describing the worst case but it could end up costing you far more than an annual increase in your insurance premium.