I was being a tad facetious but if thats not the case then are you SURE that its the overflow thats leaking? Where is it leaking from - the bit you see in the bath or the other end where it joins the waste outlet?
So you are saying that water is coming UP the overflow? One possibility is that you have a hair/soap scum etc blockage in the waste but its one hell of a long way up for the water to travel and its far more likely that it will just drain very slowly.
Put the plug in and fill bath with a couple of inches of water. Pull the plug. Does the water drain away slowly or at normal rates? If slowly then you have a blockage.
Oh hang on a moment do you have one of those combined overflow/filler mechanisms where when you turn on the (remotely sited) taps the water comes out of the bottom of the pop up waste control?
Is the shower operated by the same valve mechanism that fills the bath. There may be a problem with the divertor letting by.
thats correct - its the overflow hole on the bath.
I will give the drainage test another go (although had not notice any drainage conerns. re the shower thought have to admit I dont know how the water diverts. i know their is a pump for it it what was the airing cupboard (until i had a new boiler).