Do you mean the
real North West, or just the NW of Englandcestershire?
Assuming you want more power & some nice pipes, I'd go to an exhaust fabricator and get them to make you a bit of straight pipe to replace the rear box, and extend to show visible "tailpipes".
As detailed on tdiclub.com, removal of the rear silencer (affectionately known as a mufflerectomy) gives similar increase to sound and power as a (much more expensive) free-flow system.