Real reason for Boris 'Where's Wally' mystery trip to Afghanistan?

Afghanistan is a long way to go to avoid an embarrassing vote in Parliament.

The absence of Foreign Secretary Boris Johnson isn't the only telling thing about the Heathrow debate tonight, which stacks up to be a pretty good snapshot of the odd and confusing place our politics finds itself in at the moment.

The Conservatives officially back the policy but are corralling their MPs very strenuously to make sure they don't lose the vote after a minister resigned.

One former cabinet minister told me today the "whipping operation is ridiculous, they were even making sure I was going to be there".

But collective responsibility as it has traditionally functioned is out of the window. Cabinet ministers seem rather to have given up on trying to agree with each other (Heathrow isn't the only matter where there is very public discord).

The Labour Party is opposing a policy tonight when it comes to Heathrow that their main backer and dozens of their MPs actually support.

The Lib Dems are sticking to their principles of opposing Heathrow but with their size these days are finding it hard to make much noise about it.

And the SNP who have been officially supportive of expanding the airport won't vote because they say they haven't had credible guarantees from the government.

Clear?

All this on a problem that Westminster has been arguing about for decades. It will pass tonight, but this is only, remember, only, the equivalent of the outline planning permission - gasp.

Huge attention in the frothy end of the Westminster bubble has centred on the foreign secretary as - to his colleagues' frustration - it often does.

During the first half of the day, much of SW1 engaged in a game of political Where's Wally? Speculation on top of speculation on top of speculation about where Boris Johnson could be.

Was he still in his Foreign Office lair? In the air? Hiding in the tearoom of the House of Commons? The one place he was categorically not was chaining himself to bulldozers at Heathrow.

Then, in the end, the Afghan foreign ministry gave it away by posting a picture of the foreign secretary and his counterpart together at a meeting in Kabul.

Mr Johnson held talks with Afghan minister Hekmat Karzai in Kabul as the debate began

The mystery of his whereabouts was solved, but not yet the mystery of the purpose. Afghanistan is not exactly an easy place to head for a quick hello.

Several sources in Westminster tonight suggest there was a serious reason.

My colleague Jonathan Beale reported last month that the government was considering sending about 400 more troops to Afghanistan to join the 600 or so already there helping train Afghan forces.

Sources suggest tonight that the National Security Council will discuss the proposal tomorrow afternoon, with the government potentially approving the move, and a possible announcement in the coming days.

The soldiers would not be involved in combat, but helping the Afghans provide more security in Kabul.

It is suggested an uplift of 440 would make the UK the third biggest contributor in Afghanistan.

It is a very long way from the troop numbers during the days of intense conflict.

But a move that could give the UK more authority in the run up to a Nato summit at a time when the debate around our future defence is being intensely fought.