Suddenly have black mould in room corner - who would be able to help

[EllaSaturday]

I have just found black mould in a corner of my living room where two outside walls meet. This was not there a month ago and i don't have damp/condensation issues anywhere else in the house.
On the outside wall in this particular corner I have a drain pipe coming down.
Could there be a leak? There appears to be a little bit of water on the floor there too.
What sort of tradesperson would be best to inspect and advise me on what to do?
Please help, oh wise mumsnetters!

Sounds like it could be the downpipe - does it discharge into a drain? Also check the outside ground levels which should be below the damp proof course. Piglet john is good at this sort of thing.

Is there loads of black mould, on a visibly damp background? Or is it just a bit?

Black mould can just gather in poorly ventilated corners of older houses, particularly if washing is dried in the room or if there is a fridge nearby. You can buy special mould spray to remove it (which contains bleach, so be careful with soft furnishings around the area). However, a large area that's really bad may indicate some kind of leak. Get outside the next time it rains and have a good look at whether water from the drain pipe is getting onto the wall, or not draining somewhere.

I don;t dry washing in that room, or cook, or have a fridge...
I checked the masonry outside, and it looks like some of the pointing low down is wearing away - perhaps that is the problem? Can't see water sitting at hte bottom of the drain pipe, but then again it hasn't been raining all that much, so probably won't see until it really pours it down.

Was there something in front of the corner area while it was building up? I have found black mould in our house which has been caused by the kids piling stuff up in corners, which has meant there hasn't been enough air flow. Mould and mildew cleaner sorts it out.