to satisfy the goody 2 shoes on the forum, you can only technically legally have an EC approved cat on the car for road use. But in all honesty no one cares unless the car is going for type approval. As long as it passes the MOT no one is ever going to look at it. In fact even aftermarket standard cats offer 2 options for ex approved and non existent approved ones. The difference is with the metals they are made with internally.
From what I can find Milltek are the only people that offer a sports cat that's EC approved, problem is it's 2k. I think Wagner tuning might offer one also but it's not clear and might be a loss in translation.
Scorpion list a sports cat for your car that's not ec approved, and it's £600. The decat pipe is £320, this is probably why they went for the decat and not the sports cat.
Alternatively you could just get a 200 cell universal sports cat welded into your existing decat pipe (I've said 200 cell as that's what scorpion list, but a 300 cell cat would be lower the emissions more, but be more restrictive) this can be done at a sports exhaust shop, there is usually one close.by most places in the UK.
This would be the cheapest and most convenient option As long as it passes the MOT it will never be looked at by anyone.