Question Author
HI. Thanks both for your comments.
What puzzles me about the original comments, from a qualified electrician I consulted, even if pyro was not allowed in this kind of environment, I can't see how it could be applied to an existing installation retrospectively.
In a new installation I could see it, a bit like building regs, making changes to a building is not the same as a new build. If this was a completely new installation I could see that being applied and one perhaps one would go for SWA cables and not pyro.
The existing cable test out OK, it's buried in concrete but is PVC covered for the whole of its length. The failed cable, I have now found was damaged as it left the ground above the surface.
I will take your advice and wait to see if there are other posting on this.