I have a 1.4 16v Fabia Comfort with a vrs rear bumper and i was wondering if a milteck exhaust mid section and back box would still fit on to my car and if not what will?

No it won't fit, there isn't an aftermarket 'performance' exhaust suitable for a petrol Fabia, you'll have to get one made from generic parts, there are companies that do this but it'll be expensive and largely pointless since the standard system is excellent.