Damp on chimney breast

[oddjob]

Hi,
We have just found that the the base of our chimney breast (internal wall)is damp to about a foot high from the floor. I think our fireplace may have been filled in sometime in the past with expanding foam (?) and there are no vent bricks as far as I can see (upstairs or downstairs).
Does this sound like it could be the cause of the damp ?
Thanks.