What is this leak

[PickledWilly]

Had a plumber over today to replace some old but functional taps - bathroom basin and bath. After he had left I noticed that it was wet where the sinks waste pipe goes into the tiled wall. What could this leak be? If a plumber causes a leak will they usually rectify this for free?

Is it actually leaking or just wet from the work done today? I'd put a container under it and see if it's still wet in the morning.

Dry the pipe thoroughly and then tie a length of loo roll round it. If the paper gets wet, there's a leak. If not and the bottom of th pipe/wall is also dry then it's just wet from the work.

Unfortunately it is definitely a leak. The waste pipe that goes into the wall appears to be leaking. I tied toilet roll around the nut in case it was leaking from the but no. The water is coming out from where the cement is dark

water almost invariably runs downhill, so your leak will be at or above the wet mark. It might be dripping down from the basin, e.g. round a tap or plug, or through the chain hole.

I don't find your picture clear, but I think Left is probably Up.

Take some more pics please including the underside and topside of the basin.

Here are some more photos

I reckon it's either dripping from the tap, or a fine spray from the joint on that braided flexible hose.

Plumber returned - the pipe had been grouted into the wall but not glued in and when he had moved the sink it had become dislodged! Pipe safely glued together and no more leaks 😊