Were you offended?

He was actually referring the numbers who are crossing the ocean to get to Europe, not those in Calais.

On the news it showed an aerial shot of a largish group of people running, and they did look like a swarm.
No, I wasn't offended.

No. One of the dictionary meanings is given as 'move somewhere in large numbers'.

The media love to claim the moral high-ground when politicians of any hue use a word which would be considered perfectly reasonable if used in any other walk of life.

I am always a bit reluctant when the media seem to be inviting me to feel something - we can all think for ourselves.

I thought immediately of a swarm of locusts and hope that was not what Cameron had in mind.

What is the point of "being offended"? I've never worked it out.

Nope. There are other words he could have used but swarm fits just as well as throng or horde or crowd....

Not especially - he could probably have found a better word, but politicians are in the spotlight all the time and cannot always get it right. I say this as someone who would never and has never voted Tory, and I have no liking for David Cameron.