He said: "Can someone please stone Yasmin Alibhai-Brown to death? I shan't tell Amnesty if you don't. It would be a blessing, really."

Since then, he has apologised, saying on Twitter: "I did not 'call' for the stoning of anybody. I made an ill-conceived attempt at humour . . . I apologise for any offence caused. It was wholly unintentional."

This wasn't enough to placate Conservative headquarters. I also understand the police are taking a complaint they received from Ms Alibhai-Brown seriously.

The truth is that many of us might have made the odd sick joke about celebrities we don't like down the pub, or over dinner with friends.

Certainly, many politicians, just like many journalists, seem to enjoy black humour.

But when you send a message on Twitter, it's not like talking to a mate in the pub. If you are in any way a public figure, it's more like issuing a press release or making a speech.

The danger, as I see it, is this: you choose who to interact with on Twitter. People tend to follow people who they like or agree with. They tend to be followed by people who like or agree with them.

Politicians, for example, tend to interact (replying to or retweeting) with people who share the same political philosophy.

Even though we all know that messages on Twitter are public, it's easy to get into the habit of acting as if you are speaking to friends. But you're not. You're speaking to the whole world and, if you are a public figure of any kind, that probably includes some people who don't like you.

So before you start typing, remember this: when you talk on Twitter, you're talking to your enemies too.

(PS Jon Bounds has his own take here: http://www.birminghamitsnotshit.co.uk/2010/11/erdington-councillor-gets-stick-for-stones.html)

Edit: By the way, if you want to hear what Yasmin Alibhai-Brown said, you can go to this Radio 5 Live website: http://www.bbc.co.uk/programmes/b0070htg and open up the programme for 10/11/2010. Her comments begin 53 minutes in.

Here's part of the interview:

Announcer: "Are we in any position to criticise countries for stoning people to death?"

Yasmin Alibhai-Brown: "I don't think our politicians are. I think our human rights organisations certainly do have that right and should absolutely be speaking out.

"But for our politicians - we are in the middle of talking about allegedly what some British soldiers did in Iraq.

"I don't think they have any moral authority any more in the world to lecture anyone on human rights abuses.

"That's one of the prices I think that's paid by countries that think there's one law for us and one law for them."