Wet patch on kitchen wall

Here are some pictures of the outside wall, and the place where the downpipes go.

https://imgur.com/a/Iq5txWG

Also a couple of pictures of the ground on a place where we don't have any visible signs of dampness inside. Are those water marks normal? (It has been raining heavily for the past couple of days)

https://imgur.com/a/QeGhaPN

Added what I can gather from those pipes:

Leftmost thin pipe: recently installed waste for the bathroom sink

Left thick one: seems to be coming from rain gutter

Right one: seems to be waste for the bath and toilet in the bathroom. There is a soil pipe as well where the toilet is located but you can't see it here since it's not on this wall. I am assuming the waste then bends to join the bath waste pipe, this is the one we can see (which is right where the bath is).

What s below down there where they get to the ground -- have no idea.

please stand back and take a wide angle pic of the whole wall.

What is that light brown thing in the middle of your first pic?

Is the ground around those pipes very wet?

Wider angle:

https://imgur.com/a/VbrQq9D

The light brown thing I am not sure exactly what it is. There are two gullies or holes or whatever.. the left one only the rain pipe goes into. The leftmost thin one and the big waste pipe on the right go to the right hole (as well as the waste pipe from the kitchen sink which is running horizontally at ground level from the other wall).

That brown thing seems to be separating those two holes for some reason..

Very hard to say if the ground is wet. I mean it is wet but it has been raining so..

And the wet patch reaches part way up that window.

Let's start by considering that the surveyor was right and it's one or more of those pipes leaking. Have a good look at them and feel all round with your fingers.

if blocked, water will gush out of the socket joint in a rainwater pipe (they are made that way) but there might be a crack or hole round the back out of sight.

If you can run water down them, perhaps with a hosepipe, in dry weather you can look for signs of leaks.

I expect they are iron pipes and if there is anything wrong with them I'd replace in plastic.

Still need a photo that shows the wall all the way to the top.

You need to clear away the vegetation and scrape the soil away from those drains.

I expect you have a glazed clay gulley and a socket for the soil pipe, they are pretty sure to be cracked or broken and leaking into the ground. If so, they need to be dug out and replaced and that would be a convenient time to replace the pipes above.

When you lift the floorboards inside you may find a lot of mud if there has been a long term leak. You may find loose bricks if there was lime mortar that has washed away. If you find any bright red worms, or wild tomato plants, that is evidence of a leaking soil pipe. The vegetation I see suggests the ground is wet.

Thanks will take all that into account! I am not too keen on lifting floor boards right now since we use that room and the floorboards are beneath some sort of old fashioned vinyl flooring, was hoping that could wait until redecoration.

Replacing the gully or pipes seems more approachable, shouldn't be a big job I suppose?

What s also a bit strange is that the timber skirting boards inside do no seem bad. They are not warped or anything..

On a side note: that big waste pipe seems to be open at the bottom end before making any connection to any drain or gully. Is that ok? I am not sure toilet waste goes down that pipe but if it does, sounds like very unhealthy. We never have any sort of foul smell, if that helps.

I'd be looking for cracked or blown render, and it may be higher up the wall not just where the internal damp is