Sketch show Big Train has been rapped for showing a teacher being shot in front of a classroom of children.

But another skit, entitled Fat-Handed Twat, was cleared of mocking the disabled.

Seven viewers complained about the schoolroom scene after the show was broadcast on BBC2 in January.

The corporation argued: "The reality of disruptive pupils was exaggerated to a degree which was plainly farcical and, rather than constituting a tasteless representation of reality, or encouraging emulation, the sketch arguably contained a serious message about the growing inability of authority in a liberal society to cope with serious challenge."

But watchdogs at the Broadcasting Standards Commission disagreed.

Upholding the complaints, they said: the sketch "exceeded acceptable boundaries for broadcast, particularly at a time when school killings were in the news."

However, it agreed with the BBC's explanation that the other sketch satirised those unsympathetic to the afflicted.

The BBC said: "Far from the sketch showing lack of sympathy towards disability, the very opposite was the case."

The BSC panel dismissed the single complaint against the show, saying: "The butt of the humour was clearly not his disability but those who mocked his affliction. "