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When prime ministers travel abroad, more often than not crises blow up at home.

There then ensues a frantic process whereby Downing Street officials desperately try to find out what is happening.

They get their wires crossed. And then they make poor decisions. A row follows.

The prime minister gets cross that his trip has been overshadowed by a domestic news story. And he skulks down the front of the plane as far away from the hacks as he can get.

Not so today. David Cameron bounded down the plane almost as soon as we took off with a grin on his face.

Yes, of course he wanted to talk about the Middle East. But the source of his cheerfulness was Labour's opposition to an automatic in-out referendum.

This is what he said, pretty much as a stream of consciousness answer to one question: "It is not a proposal for an in-out referendum. This is a policy clearly designed by a committee who couldn't agree what to do and they have come up with a policy that makes no sense whatsoever.

"The British people now have a very, very clear choice. At the next election they can elect a Conservative government that will renegotiate Britain's position in Europe and give people a guaranteed in out referendum by the end of 2017.

"If they get a Labour government, they will get no referendum, no choice, no reform, nothing. It couldn't be clearer.

"When you read that article, it was all a bit confused overnight in their attempted briefing. If you read that FT article, it is absolutely clear, if you get Miliband, you don't get a referendum.

"You don't get a choice. It is the classic Labour "we know best" approach to politics."

Politicians love issues that distinguish their party from their opponents - they are called "dividing lines" in the argot of Westminster - and there could be few bigger than this.

But if Mr Cameron arrived in Israel with a domestic smile on his face, it did not last for long. He has waited almost four years to visit Israel as prime minister, a fact that has not gone unnoticed here.

A trip that was delayed by last months floods has now been met by a strike by Israeli foreign ministry workers who are upset that he has come.

The prime minister admits that the trip is "relatively brief" but insists it is important nonetheless. His aim is join a growing list of western leaders trying inject momentum behind the US diplomatic attempt to get the Israelis and Palestinians talking again.

He said he wants to encourage both sides to take what he calls the "bold and difficult" decisions needed to achieve a two state solution.

The latest deadline - there are always deadlines in these processes - is April and diplomats see this moment as a window when leaders such as the prime minister can make a difference by urging all sides over the line.

Like most visiting dignitaries, the prime minister will visit the Yad Vashem memorial to the holocaust and lay wreath in honour of those who died.

And in his speech to the Israeli parliament, he will talk about his own Jewish ancestry, namely his great grandfather, a Jewish banker who came to Britain 150 years ago.