stop-tap

Evening all. After suspecting for years that our property never had an internal stopcock when we fitted the bathroom a couple years ago, I recently had the kitchen plinths out to investigate some rodent activity and set some traps and I ended up finding a lead pipe in the far corner which the...

I am looking to replace our inside stop tap, but the outside isolator cover has a square headed inset, which frustratingly is smaller than a 3/8 socket adaptor... This is what is looks like: Does anyone know where to get the tool to unlock these? Cheers.