Bought a 1999 S80 2.4(140bhp) three years ago with 64k(miles),This car has always suffered from pre-ignition knock (pinking). First advice was to use a higher octane fuel, which has only reduced the pinking. I decided to take it back to the main agent / dealer, who after four hours of diagnostic work reported that there was nothing wrong with the vehicle. Since then I've replaced the spark plugs, knock sensor, air filter, and checked replaced the coolant cleaned the throttle body etc.

The car still pinks, normally under light load / acceleration and is worse during hot weather with the air con active.

I'm now at a loss as to how to resolve this issue, I am considering investing in a BROQUET fuel catalyst.

Any suggestions would be appreciated

What you are talking about is "pinging." This is caused when the fuel/air mixture is ignited prematurely. Advanced ignition timing can cause this. First make sure your timing is set right. Another cause can be carbon buildup in the cylinder and head area. The carbon retains heat and can become a "hot spot" that ignites the mixture before the spark plugs do. There are some over-the-counter products you can try to remove the carbon, such as Techron Concentrate, SeaFoam, or STP Complete Fuel System Cleaner. If that doesn't work, you'll need to tear the engine down and scrape out the carbon by hand.