Damp in my Victorian cottage

[sian]

Hello,

There are several areas of damp in my house.. The ground level kitchen cupboard smells of it, ( thus is near a closed fireplace which leaked just one time when it rained and never again as far as I can tell, the bathroom wall in a cupboard (pictured) and the downstairs toilet outside facing wall ( pictured) I get slugs fairly regularly which I read like the damp. Where/how do I start rectifying this? I'm terrified of the cost Thanks