I bashed out the cat a couple of weeks after the tune because I noticed that the material inside had come loose and was rattling around a lot. After i did this I called the workshop that tuned my car and asked if i would need a retune due to gutting the cat. I was advised that after removing a cat a retune is generally not required. However they weren't to know that at the time of tune the cat may have been partially blocked. Maybe it was blocked then or maybe it got blocked after, who knows. But perhaps with that information I would have had a different response from them.
Anyway like I said lesson learned.