No you don't have a dirty mind.

This is REALLY from a kids show from the UK.
Since this has been going around the Net for a while, here's the real score:

"it was filmed as a joke and never intended for public consumption. There was a great tradition at the BBC and ITV companies of the videotape editing departments compiling tapes for their christmas parties - including clips with shows shot especially for the internal tape.

It was recorded in 1979, when the show had been running for several years.
It was never intended to be shown on TV. In fact, the sketch was performed simply for the amusement of the cast and crew, and would have been lost to history, were it not for the
OBA 1 Christmas tape put together by Thames TV engineers."

Source: http://rainbow.arch.scriptmania.com/rainbow_tv_episode.html