Downpipe
 

If replacing decat downpipe with a sports cat downpipe would a need a remap and where is the best place to buy a gasket for between the turbo and downpipe as mine sounds like it's blowing .

Import car parts do a kit consisting of downpipe to turbo gasket, the donut that goes between the down pipe and centre box and a set of nuts, studs and bolts for the turbo.
Don't know about the remap but I'd assume that as it will be flowing a lot better that the restrictive standard pipe it would be advisable. The only thing that may stop that is if you still have the centre CAT fitted, I've done my downpipe and left the centre CAT and the fuelling was spot on when it was on the dyno the other day, UK classics tend to run a bit rich anyway so a filter and downpipe leans it off a bit.

I think it's a good buy for the gasket kit as it comes with everything you need I have a full decat system on already mapped to the car I was wanting to put a sports cat on so that I don't need to keep changing for MOT's .