can you isolate the tap at source ie is there a valve under the sink/basin ?? if you can turn the water off there you then have take the tap apart starting from the top take the handle/body off you should see a nut at the bottom turn that and remove the spindle yuo should see the washer chgange that now you need to have a tap reseating tool this removes all the crap from the face inside the tap once see the tap reseating tool youll know how to use it once that is done rebuild the tap hope this helps tools needed philips screwdriver,adjustable spanner and tap reseating tool
plumber1722
February 2011