A lot more than you’d think, is the initial answer.

As we are all increasingly aware, put-upon insurance companies are looking for more and more ways not to shell out and one of the main ways is to prove that you were the one that was at fault- either through negligence, or failing to declare a variance in your vehicle to what was set down on paper.

And most of us have witnessed the hike in premiums after they have shelled out. Just ask any home-owner on the Somerset Flats.

Granted, we would all at least understand -if not entirely agree- with increased premiums if we had in some way improved out car’s performance, but digging a little deeper turns up some surprising turnips.

There are two main areas where car mods are assessed in coming up with a premium. ‘Risk of Theft’ and ‘Risk of Accident’.

So, Risk of Theft would be increased, at least in the insurers eyes, if you were to add things to your car that are of value, such as superchargers, beefed up exhausts and the like.  But it would also include surprising things like a sat nav or phone kit, making the car more likely to be broken in to.

Risk of Accident involves things like engine alterations, car body-kits or body alterations- like brakes, or even sports seats.

But this goes even further, to paint jobs or decals. Statistically, the drivers of these cars are in more accidents more often, or have their cars damaged or stolen. Are they pickin’ on the youngsters? Well, yes they are, but they do have the stats to back it up.

Insurance will start to ramp quite noticeably if you start talking roll cages, replacement of seats, steering wheel or dash. It’ll get worse if you mention bodywork alterations, like bonnet scoops, wheel arch or wing flares.

Then there’s transmission or gearbox changes and, if you really do want to push your premium into the rarefied upper reaches of Earth’s atmosphere, add a blower, turbo or nitrous kit and watch it skyrocket.

Interestingly, wider wheels, or replacing your current ones with alloys is a tiny increase of only 1% if any, with most insurers.

But there are some mods which can actually lower your premium with some insurers. A tow bar indicates that you will mostly be travelling at 50mph when doing your beans, which they like very much. Even if you hate caravans. Parking sensors is another, as they see these (statistically) as vastly reducing bumps and scratches. But there are precious few. Nearly every other mod you can come up with will only add to the pain.

And don’t be thinkin’ that simply by sticking an inordinately ostentatious chrome tow bar on the back of your bangin’ Subaru, it’ll somehow offset the ‘charger sticking out ‘the bonnet. It won’t.

Different insurers regard different mods differently. If you really do have a monster, it’s without doubt best to go with a specialist insurer, fit for purpose. This applies particularly to car clubs and the like, where although your ’64 MkI Lotus Cortina is your pride and joy and only comes out if the forecast is sunny for a fortnight, less imaginative insurers will only see a rare, expensive race car with the wrong lump under the bonnet. Not to mention the upgraded brakes, the roll bar, the go-faster stripes…

The bottom line is, whatever you do that takes your car away from perceived standard, let them know, or they can -and will- use it as a basis to nix any future claim.

Some insurers will even go so far as to say that any alterations extra to the factory spec, even when fitted by that factory, come under the heading modification. I’m talkin’ leather seats. Yeah, I know.

All this being the case, ‘full disclosure’ means just that. And, when buying ‘pre-loved’ especially, I would strongly advise you make sure that thorough checks are made to that vehicle upon purchase, thus preventing any ugly surprises if you do have cause to file a claim.