alkathene/outside stop cock

[amstel]

Hello everybody,
I live in a 1950,s bungalow, and my inside stopcock is leaking slightly along the spindle, also it will not completely close of the water, probably the seal I suppose,as the spindle is easy to turn.
The incoming black pipe is alkathene I think and the o/d is approx 21-21.5mm.
I intend to use a new 22mm stop cock with a 3/4" olive on the alkathene, and 22mm copper on the out, reduced to 15mm to join up with the existing 15mm rising main.
Can i get inserts for the alkathene, or is it a piece of 15mm copper as the insert?
Does this sound ok, I know about philmac universal couplers, but i,m sure I can go straight into the new stop cock?
Thanks in advance for any advice.

 

[Burnerman]

You could consider refurbishing the existing stopcock if you want - the fact that it won't stop the water flow just means that it needs a new rubber washer, and the spindle leak can be sorted by either tightening the gland nut, or by maybe repacking the gland first with ptfe string.
If you can turn the water off in the street, and the stopcock body unscrews ok, its a simple, quick job.
John