Two big anxieties hang like dark clouds over the voters’ minds this November. Neither has anything to do with party politics. One is Afghanistan, the other the collapse of confidence in Parliament. The first, the Afghan war, is raw, ominous and impossible to ignore. Events this week give it a cruel new urgency.

The second anxiety would not be high on a list of public worries, but nags in the background, like the thought of dry rot in the roof.

Our generalised feeling that the House of Commons is unfit to discharge its responsibilities, and our particular rage over MPs’ expenses arises not because we think democracy doesn’t matter, but because we know it does.

Beneath public disquiet about the expenses scandal an underlying disquiet feeds the aggression: a reason we are looking for sticks with which to beat MPs. It’s because we don’t just think they’re greedy, we think they’re useless. Gurkhas excepted, it is now a very long time since the Commons offered the nation any substantial or sensational demonstration of what Parliament is for.

I know, I know. Before you wise old Sir Owls of the senior backbenches and you energetic young constituency Members round on me I concede that MPs do wonderful work helping to solve constituents’ problems; and stalwart, unshowy work scrutinising legislation away from the chamber. But a House of Commons has to be there for something more. It must be able to crack the whip; or we would recruit MPs by other means than the hustings.

Parliament is supposed to intervene in history. Not often; not lightly; and not without a very proper sense that 650 men and women cannot drive — as a driver drives a wagon — the huge pantechnicon that is a modern state.

But what if the wagon is going totally the wrong way? There are times when governments just get it wrong — and get it wrong big time — for reasons of pride, ignorance, or perceived constraints. They half know this, but box themselves mentally in, losing the will to break free. I’d cite, for instance, the poll tax, a groupthink blunder by the Tory leadership into which many at the top were drawn. As the disaster unfolded the argument for the poll tax was lost in Commons minds and hearts, years before the Cabinet caught up. Perhaps MPs owed the public an earlier rebellion on the subject. It didn’t happen.

On Iraq there was a vote; but a threat from Tony Blair (probably bogus) to resign, and a speech that was as spellbinding as it was sly, narrowly won a nervous Commons over. The MPs should have called his bluff.

People need parables. One clear and shining example of the good a man or an institution can do may exert a stronger pull on the public mind than a hundred small instances and arguments. Gordon Brown’s premiership would not now be rescued even by the coming-good of all his myriad initiatives; but if he dived into the Thames and rescued a drowning child at Christmas he’d be in with a chance again.

Parliament cannot rescue drowning children. But it can rescue a flailing British Government from waters into which it now knows it should never have got, but sees no means of climbing out. Parliament can rescue the hundreds of troops who have still, undoubtedly, to die in Afghanistan if we push on like this. The time has passed to rail against Gordon Brown, Bob Ainsworth — and indeed David Cameron and Nick Clegg — for having supported Britain’s entry into this war. To them and to many principled and intelligent people it seemed a good idea at the time.

No longer.

Believe me, for I have not a shadow of a doubt: you have no need to persuade any of our top politicians that we British should never have piled into Afghanistan. They know. Everybody knows. The military know. Even the neocons know. There’s hardly a soul left in the upper reaches of British politics who, granted a wish to rewind history back to early 2006 and Britain’s decision to accept command in Helmand, would argue for doing it again.

So why won’t they admit it? There are two very good reasons. Such an admission has consequences: either pull out now and kick a major prop from beneath our American allies; or carry on regardless, supporting them while having publicly admitted that the game’s up.

This latter is unthinkable. Imagine how it would then sound for a prime minister to continue reading out the names of the dead in Parliament, or an opposition leader continue paying tribute to our brave boys’ courage.

Yet to leave the Americans in the lurch would be extraordinarily difficult. “Why? And why now,” Washington would ask. How could a British prime minister reply?

Like this. “Barack, you’ll have heard of last week’s Afghanistan vote in our House of Commons: a major rebellion, on a motion expressing doubt on the strategy and asking ministers to reconsider the options, including a phased withdrawal.

“I can hold the line, Mr President, for a month or two more; but we’ve got to start talking to you about either bringing troops home, or back at least from the Helmand front.”

Few believe President Obama to be privately gung-ho about this war, and such a development might even ease the pressure on him. By giving Mr Brown or Mr Cameron an external constraint to counter the pressure they face to plough on, it could offer a useful ladder to climb down.

In the months before the Iraq invasion, George W. Bush told Tony Blair that, given Mr Blair’s difficulties with domestic opinion, he would happily waive his request for British troops. The lesson is clear. When it comes to scaling back our military support for Washington, a prime minister can better save face if everyone knows one arm is twisted behind his back. This Parliament could redeem itself, or the next establish itself, by doing the twisting.

Parliament should be for us both a sword and a shield. The shield looks broken and the sword is blunted. Committees of inquiry into parliamentary expenses can report and be bowed to until kingdom come, but until Parliament puts its armour back on, accepts a challenge and does something big, brave and useful, the public will only spit. Just such a challenge stares MPs in the face.

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