In article .uk,
Ed Sirett writes
i'd quite like to understand why this joint has failed so spectacularly
before i go trying to fix it.


Either the pipe was not inserted past the olive (it may have been but then
pulled out before tightening), in this case the tightening tends to roll
the olive over the end of the pipe and tends to expel the pipe.

The fitting was in noway adequately tightened.
If the pipe/fitting are in good alignment and everything is clean then the
back nut will "finger spin" up to the "bite point". After that I would say
you are looking at adding 2-4 'flats' (1/3 to 2/3 of a turn to tighten
most fittings).

The voice of reason from one who does this for a living, respect.
--
fred
Plusnet - I hope you like vanilla