Years ago I did the honest thing and told the insurance company I was changing uprating the brakes to disks from drums on the front on a mini and then later changing the engine to a 1275!
They dumped me on the spot and left me unable to drive it.
I then had to have an engineers report done on the car which came back 100% OK and then got insurance on it! :shock:
A bloody pain!
Then again a work friend didn't tell his insurance about his modified Punto turbo with drilled disks uprated hose's exhaust etc and when he did have a small crash - not his fault, he went to court and got fined and lost!
He is still not driving now as it would cost to much and he has lost interest!! this was 4 to 5 years ago now.
I think any modification from standard is classed as a mod even if the engine is swapped for a lower cc.
It seems making a car slower or safer will not count as it depends who does the mod and if the company insure modified cars like Arian Flux who will!
Who knows how they come to some of their decisions!
I lost an insurance fight when I got hit by a driver who had just passed their test doing an overtake on a car which was pulling in to a junction I had just come out of (Also the driver in the road pulling in to where I wanted to come out had to wait for me to come out before he could fit in so was slowing down) there was only room for 2 and a half cars to pass in the main road and I was on the correct side of the road and got hit behind the drivers door! She (yes she!) decided to go down the middle! This was in an industrial estate and the limit was 30 and she was not doing 30! Hence her decision to go through the middle.
The road I pulled out of was also up hill so I could not see her until I was fully out of the junction which is where I was when she hit me. The amount of people I see who are so far up the cars boot in front that when the car turns in to a side turning the car following has to pull out in to the middle of the road to miss hitting it is LOADS!
I lost because I pulled out!! Yet I was up against the curb and parallel to it and nearly stationary, but she could not stop or fit through the gap!
Cost me 3.5 years no claims and the side of my 1275GT (That was after the engine swap and disk up grade.
After that I went protected no claims
I think sometimes insurance companies do deals with other companies but no prove on that.