The Pre-cat sits right next to the turbo and was introduced for cold weather starting emissions in Germany - it's not a UK requirement.

Removing the Pre-cat is a Simple enough job.
Helps to bring down EGT (Exhaust Gas Temperatures)'s, especially good for K03 GTI's which don't have the K04's twin scroll design.

The mod releases a few extra horsepower, a little more noise, and MOT friendly.