Damp problem, to middle of inside of Bay on Victorian Terrace- Cause?

I have a damp problem on the inside wall adjacent to bay on ground floor front room of victorian terraced house. The damp area is approximate 50-60cm squared and begins around 1m up from the floor and stretches from the bay window across to the inside wall. The damp area is mirrored on the outside of the building, where the bricks and mortar appear damp, even when not raining. The area that is damp on the outside has been repointed/repaired at some point in recent years (i moved in 6 months ago, so before then). What could the cause be? There doesn't seem to be a problem with guttering. Could it be the pointing itself?