All I can say is that despite what logic says, I merely turned the in line
water tap on the cold feed back to reduce the flow rate and no more
dripping.
Brian

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The Sofa of Brian Gaff...

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I have the same problem.
Switched from conventional tap inserts to disc.
No problem, but now our cold water pressure is higher.

Neither tap drips, but if I turn on the cold tap, the hot tap starts to leak
slightly until you turn on the hot and then off.
Turning on the hot tap does not make the cold tap leak.

Nothing to do with dirt or limescale. A new insert does the same.
Swapping the inserts (cold and hot) and the hot still leaks slightly when
the cold is turned off and then on.

The problem I believe is caused by the high pressure on the cold side being
applied to the base of the ceramic insert and moving it slightly out of
position. My guess is that it moves the upper disk slightly (there is
tolerance between the key slot in the ceramic disk and the tab on the
spindle that fits into it.
The problem started when they built a lot of houses near us and they
increased the cold water main pressure.

This does not happen on another tap where the hot and cold have different
channels up the mixer spout and the cold water pressure is not applied to
the hot insert.

My options:
1) Go back to ordinary washers.
2) Pressure reducing valve - not worth it.
3) I am going to file the edge of the insert spindle to allow it to move
about 1 degree more when off. This gives a slightly increased overlap
between the disks. This is an experiment and I don't know if it will work.

I will try "3" first. then opt for "1"

By a process of elimination it is the low temperature hot water side (of the
tap) that is the problem. It is not the seat (the leak would not stop when
the hot is turned on briefly then off)

Hope this helps.

I anyone knows better let me know.