Tends to very between seasons (the show does move to a pre-watershed slot sometimes) most of the time there is very little swearing. It would be bleeped whenever Dave reruns the series.
Nothing major really. The show doesn't tend to be that profane, and is pretty tame compared to other British panel shows such as 8 Out of 10 Cats, Never Mind the Buzzcocks, and Mock the Week.
The earlier seasons contain much more stronger language than the later seasons do because they aired post-watershed. While the show still drifts to post-watershed slots at times, the language has never really drifted up, if at all.