Another daft question, (thanks for all the screwfix shop replies - works
a treat!), but the incoming mains to our house is a black semi-flexible
pipe of about an inch in external diameter. This has what looks like an
odd coupling that looks like some sort of compression joint to 15mm pipe
where I fitted a stop cock some years back... (works fine).

Our water pressure is high (8 bar), but flow rate low (under 10 litres
a minute) I think due to some external restriction in the pipe work -
which I'm not prepared to dig up at this point in time.

I'd like to remove the join to the 15mm pipe, fit a coupler to 22mm pipe,
a quarter turn full-bore "stop cock" to make it fool-proof for wifey,
then fit a pressure reducer to 3.5 bar, and then run 22mm pipe from
there - hoping to get a better flow rate at a pressure that'll reduce
the possibility of burst pipes (not a plesant sight round here when it
happens - as it did to our neighbours recently)

Googling finds various names for plastic pipe - mostly seem to refer to
blue alcathene or MDPE pipe, but I'm not sure that's what I have. It's
black!

So can some kind soul tell me the name/official size of the pipe and
suggest a coupling device?

Thanks,

Gordon