Sky News apologised yesterday after a presenter joked on air that the Conservatives favoured a policy of “extermination” for immigrants.

Julie Etchingham’s humorous aside was broadcast accidentally during live coverage of David Cameron’s first significant speech on immigration.

Mr Cameron said: “Let me outline the action that a Conservative government would take. As we have seen, some of the increase in population size results from natural change – birth rates, death rates. Here our policy should be obvious . . . ”

At this point Ms Etchingham was heard to say “extermination”.

Sky News apologised after the gaffe and said that Ms Etchingham’s comment was regrettable.

Ms Etchingham, a former BBC journalist, is leaving the broadcaster to co-present ITV’s resurrected News at Ten bulletin with Sir Trevor McDonald.

A Sky News spokesman said: “A comment was made in the studio during David Cameron’s speech that was broadcast in error. The comment was not intended for broadcast. The off-the-cuff remark was regrettable.”

Microphone mishaps have caused embarrassment for several British political leaders. John Major, when Prime Minister, was picked up by an ITN microphone referring to his Euro-sceptic colleagues in the Cabinet as “bastards”.

In July last year, during the war between Israel and Hezbollah, President Bush was caught using very undiplomatic language in conversation with Tony Blair. The President greeted the Prime Minister: “Yo Blair. How are you doin?” before adding: “The thing is that what they [Russia] need to do is get Syria to get Hezbollah to stop doing this s*** and it’s over.”

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