Kinda desperate for a solution to the sheer shit show I'm facing.

I work in a court in the UK as the maintenance guy/handyman, you can probably guess who I work for from that. I have a job where the isolation valve on a pipe is leaking. Fairly badly in the closed position and a steady stream in the open position, it's already causing damage to the basement and slowly flooding it.

There's no isolation that I can find and none of the hmcts gremlins in the office can give me a plan for the piping. I tried to install a aladdin isolator onto the pipe but while it installed fine something bound up and it's pretty much useless.

Now they want me to install a standard 15mm isolation valve onto a live pipe with no backup plan, I'm the only person permanently on site so all the responsibility, consequences and shouting end squarely with me.

I'm not a qualified plumber, is there anything else I can try or should I give them the offer of "hire a plumber from the contractor list or take my resignation with immediate effect"?