Not sure what the EPA is RJ, but the UK regulations regarding railways, particularly steam ones, are very comprehensive.
The major factor in Tornados favor is being a new loco she has had all necessary requirements made/fitted during the building of her. Of all the steam locos in the UK that have been restored or preserved only a few can run on our mainlines. Those that can't are restricted to the many Hertitage lines we have over here.
Another factor, which I think has been also mentioned elsewhere, is that as a new loco she can run at up to 90 MPH making her the fastest operational steam loco in the UK and that is, most certainly, a crowd puller.
I am sure TAC or one or two others could furnish more facts and some percentages. I can't.