But the stopcock wont fit directly onto that big nut, as stopcocks have a compression fitting which is incompatable with the nut. I very much doubt there will be stopcocks which will fit directly onto that nut anymore!
I'm assuming that what is going to be needed is a threaded fitting adapter which goes into the big nut, and can then be fitted directly to a new stopcock.
That round section will probably still be the gland nut, it just isn't a HEX end, does it look like it should screw out? If so a pair of vice grips will be needed.
Chop it off and stick a UTC on the steel pipe - you'll need to hack a bit of wall away behind the pipe for clearance. Make sure all the new stuff is 22mm to provide a bit of future proofing.
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