Just want to no what decat downpipe I should get 

Have you considered the MOT implications in removing your catalytic converter ? 

Yes just means I have to swap it over before MOT everytime 

4 hours ago, sebg said:

Yes just means I have to swap it over before MOT everytime 

The problem with that is, you're not the only one doing that and certain organisations are already highlighting that despite all the UK & EU legislation and the fitment of DPF's/GPF's/AdBlue et al, emission levels are still increasing and the only way to really deal with the problem will be the introduction of vehicle no go zones, which a number of cities and towns are already implementing.