Hmmm... is it fluffy? I have read that it depends on the type of mould as to how you best remove it. I've also heard that bleach will be a temporary solution but it will most likely grow back as it won't be able to kill the "roots" of the mould deep in the bricks.

I think the first thing you need to do is work out where the humidity is coming from and deal with that... mould needs about 50 - 60 % air humidity to grow. Are the bricks near a bathroom or kitchen?

If you are really keen you could get a mould specialist in who will take a sample of it and determine what kind it is. Most moulds put spores into the air and this can result in allergies too.

Maybe Google to either find a treatment or a specialist... but one thing you can do straight away is start to improve the humidity... make sure the area has good venitlation etc. You might need to buy a dehumidifier.