Hello, I can see some mould (possibly due to damp) around my kitchen cooker hood vent as shown in the attached image. Can anyone advise what could be the cause of this and would it be costly to get the damp issue fixed. Thanks in advance. 

That looks to me like it is set up as a recirculating hood, not an extracting hood (look outside to see if there is a vent outlet)

 

If so it will just be blowing the warm moist air out at the top of the "chimney" (you will see vents on the side of it)

 

If it is recirculating it should have charcoal filters on the fan intake if you remove the grilles.