On 3 Sep, 20:58, "R" wrote:
"nafuk" wrote in message

...

Hi, I have a plastic stopcock connected to the 25 mm blue water pipe
(compression joint) and 22 mm copper (pushfit joint). The leak is
between the the grey tap section of the stopcock and the black part
that screws into the grey stop-cock part; the black part accepts the
blue pipe which is clamped by the other part of the compression slid
over the blue pipe.

The surfaces that meet are smooth and there was a residue of a gasket
when I took it apart.

I tried a large diameter fibre washer but it still leaked.

What can I use to stop the leak?

Is there a pipe insert in there to prevent distortion of the pipe when
tightened *?

Such as...http://www.screwfix.com/prods/14371/...-and-Fittings/...

Yes inserts have been used. The leak is not at the MDPE pipe
connection but rather between the stopcock body and the female part of
the compression joint. The female part screws into the stopcock body,
the mating surfaces of which are both flat.
I may just try some contact adhesive.
Cheers.