I had someone complaining that they could hear the cold water tank filling up in their loft after I fitted a new brass ball valve 🙄 think the old one must have been so slow that it didn’t make much noise.
The brass ball valves on sale now are poor quality, I had 2 fail earlier this year so I...
BSP is British Standard Pipe, it’s a name for a type of thread.
Go down Screwfix and get this, hopefully your tap head will fit it.
The washer on yours is probably coming off because the central hole maybe too big.
I use this type now in cold water storage tanks, much quieter when the tank is being refilled, also the quality of the brass type with a float seems to be really poor.