Thankfully, it didn't happen.
This morning, Ellie commented there was a strong smell of petrol in the car. I thought it was probably another car in traffic, as it disappeared as we moved away from the lights, but it persisted.
A quick investigation showed the pipe to the fuel rail was wet where it passes through the foam sleeve, next to the water hose at the back of the engine (s2 TurboCT).
I drove the 30 miles from where we were to my usual garage, opened the bonnet, to find a fine jet of fuel spraying from the pipe, aimed straight at the turbo.
This did not strike me as a great state of affairs, so I hid for a while, until the residual pressure died down and everything cooled a bit.
Replacing the pipe itself was easy enough - both ends are possible to reach, although the bulkhead end wasn't great. An inspection of the old pipe showed that it seemed to have chafed against the jubilee clip on the water hose, and rubbed a small hole. When the engine was stopped, there was a good inch between the clip and the fuel pipe, which was thoroughly clipped in.
CHECK THIS ON YOUR XM.....
Turn the jubilee clip so the pipe has no edges to rub on. Adjust the foam to provide most protection. Make sure the fuel pipe is properly clipped. I was lucky.