Unsure if I have an underground water leak

I live in an ex local authority end terrace house. I am unsure if I have an underground leak from a water pipe? Scottish Water tell me they can't help as there is no loss of water pressure and it's beyond the pavement.

The tarmac at both corners are often damp, the front corner looks like the tarmac has been replaced at some point in the past.

There are no damp patches inside the house although items in a bedside cabinet in the corner of my front North facing bedroom had mould on them. There is no sign of mould anywhere else in the house.

I can smell damp in the corner of my bedroom, in my front hall and inside my kitchen corner cupboard. I checked under my kitchen cupboard and there is no sign of damp. This is also a South facing wall.

I've been using disposable dehumidifiers for months now and not sure what road to go down. I have gutters maintained but wonder if this could be the problem or something more serious? Any advice is appreciated before going down the wrong route.

 

No, no water meter.

 

I understand. You don't think it could be the gutters then? Thank you

 

The photo was taken yesterday and it's been scorching so I don't think it can be the gutters. Your advice on getting the detector sounds like the way to go. THANK you

 

I jus couldn't understand how I can smell damp in the front hall where the stairs lead right off it. My toilet is at the top of the stairs but there's no sign of damp in there. There's also a small canopy above my front door and I have 4 steps up to the door so I gave anout 2 feet foundation under ground floorboards.

 

We've had great weather and that photo was taken yesterday? It doesn't hold water but it can turn green with algae. I tend to put salt or vinegar on the area to kill it.

 

The front of house is north facing. This photo has just been taken where you can see the damp patch. The other corner is the back of the house which is south facing and is currently dry.

 

Hi James, the down pipe was replaced about 5 year's ago as there was a hole at the top. I thought that was the cause of the problem. There is a crack in the path and I have a hedge close by. I wonder if roots could cause a problem although it doesn't go directly to the corner of the house?

 

No manhole cover in my plot James. It's at the other end of the terrace of six houses. That's flagstones and pebbles surrounding the path.

 

Could council tree roots cause damage this far away?

 

Thank you.
I feared I'd have to do that as I think over the years, this wall will be damp reaching up to my bedroom as I can smell damp in the corner. It's a downward gradient so likely the water is draining downwards. My windows are the only ones with condensation too. Would you have any idea how expensive an investigation would be and what kind of professional I need to contact?