Ricky C wrote:

How vital are inserts with pushfit plumbing with 22m acorn pipe?

I just did a very awkward plumbing job under my floorboards: I
installed two push-fit stopcocks in the main send and return of my
central heating system. After doing the job I realised I had forgotten
to use the stainless steel pipe inserts in the ends of the 22mm Acorn
pipes that went into the stopcocks.

The joints are not leaking at present, but are they likely to become
leaky in future? How vital is it that I take the floorboards up again
and redo the joints with inserts in the pipe-ends?

AIUI, the pipes will eventually 'creep' and the pressure the fittings
exert on them will squeeze them enough so tha the fittings are no longer
secure.
Whether they fall off completely at this point, or start to leak, depends
on luck and the design of the fittings.
Sorry.

For cold water, you might get away with it.