I'm looking at reinstating a 15A spur to a socket in our kitchen for an
oven. The previous owner had an all gas cooker which (I guess) whould
just have been plugged into the ring main for any leckie it needed.

There's an existing cable with plenty slack terminated under the kithen
floor connected though to a 15A fuseway in the fusebox. The cable looks
quite old, slightly heavier than 2.5mm2 (based on my vernier
measurement) and the earth is twisted steel (?) strand rather than
solid copper.

I'm pretty sure I'm going to rip it out and run a new cable just to be
sure, but before I go to all the trouble (and it will be a lot of
trouble) is there anyway to test the integrity of the existing cable?

How do I tell if it's got the old friable insulator on it?