I suggest replace the tap as internal issue.

replace washer first to see if that fixes it

O-ring seal needs replacement. Can buy the full kit from Reece with washer/ o-ring and fiber sealing washer. If would be faster and better option to replace with an Arco washing machine stop, just need to turn water meter off, drain water service at the laundry trough tap, remove old tap, thread tape the point coming out the wall- 10 times round clockwise usually does it and screw the new tap on.

tip- make sure the seal is in the washing machine hose before you reattach to the arco.