Using a fitting that can be slid entirely over an end of a pipe would help if it's easy to undo so I wondered if jg speedfit couplers had a plain 15mm bore all of the way through so that they could be undone and slid entirely onto one side of a joint leaving a bit of a gap ...
https://www.screwfix.com/p/jg-speedfit-15stvp-stop-cocks-15mm/11400 A sheared off valve. The one star reviews show it's not a unique problem. The story goes like this: You have a small problem. You turn off the stopcock to fix the problem. The stopcock shears off and starts...