I have just had this message on my car, a 51 plate jobbie, and the garage said the same thing, but without the gleeful smile. I'm told it involves replacing the front exhaust downpipe and the particulate filter. I have the bill in front of me. It quotes £139.42 for the pipe and £74.60 for the filter, all plus VAT and plus fitting of course. They also topped up the eloys fluid. They managed to break a seal, another £11.44, which I think is a seal between the pipe and the filter. All told, including a half-price MOT, I had a bill for £354.90!