tap leaking below top hat washer

[clarekeast]

A friend's cold (mains water) tap is leaking immediately below the top hat washer under the basin. I wish to attempt repair. Please let me know the procedure and tools needed. (I have a little experience so am not working totally in the dark).

Many thanks. Clare Keast

 

[MANDATE]

When you say below the top hat washer, I take it it's not the tap that is actually leaking.
Water goes from the pipe into the tap by means of a 'tap connector'.
The tap has a threaded part so it can be secured to the basin and the 'tap connector' has a nut that is screwed on the end of this threaded part.
To make the joint water tight there is a fibre washer put inside the tap connector so it might just be the nut needs tightening a little.
Because of it's positon you may need a special spanner called a 'basin wrench', there are different types available ranging from £5 to £20 but they all do the same job
Sometimes a flexible tap connector is used in the same manner but the washer will be rubber.
If you can't stop the leak by tightening, then you may have to turn off the mains water and undo the tap connector to see if the washer is perished and replace it. I've known some old ones not to have a washer but to have 'hemp' wrapped around the spigot in the tap connector.
Always be careful when tightening tap connectors because there is the risk of turning the tap.( I always hold the tap to prevent this)
Hope this helps