This is a new one. I've checked miataforum, which I consider the largest technical repository of MX5 faults (Miatas, MX5s and Roadsters should be identical as far as fuel lines etc go). There doesn't seem to be any reports of fires due to leaking fuel lines.
Heres a description of the fuel lines in the engine bay:
http://forum.miata.net/vb/showthread.php?t=304161&highlight=fire+gasoline
Even when there is a huge leak onto an exhaust, the fuel is difficult to ignite:
http://forum.miata.net/vb/showthread.php?t=207482&highlight=engine+fire+gas
Obviously, we ned to see the technical report from the Fire Brigade; is it worth getting someone from Mazda UK to look at the car.
Because this is so an unusual occurence, I can only conclude that:
1. This was an unlucky, one-off occurence
2. This is an age-related failure. This does seem unlikely though. Yours is not the oldest MX5 around by any means.
3. This is a problem peculiar to Roadster imports. Roadsters use identical fuel system parts to UK cars, and very similar materials to most Japanese cars. Therefore, possibly a deteriotation in seals during shipping. This not only a concern to owners, Mazda, but also VOSA, who regulate the importation of non-EU cars.