Jack Straw boasts that he could have stopped Britain taking part in the Iraq war, talking to Michael Cockerell in his documentary on the Foreign Office, one of his "Great Offices of State" series on BBC4, broadcast on Thursday. The obvious response is, why the hell didn't you then? But Straw's statement raises other pretty profound questions of the kind that our media never ask.

Straw is of course right. Had he resigned as Foreign Secretary and explained why in the House of Commons he would have stopped Blair's enterprise in its tracks and Britain would not have the stain of an illegal war and countless lost and maimed lives on its conscience. Lord Goldsmith could equally have prevented Blair going to war, as could the rest of the cabinet. That's the way of it in our constitutional system. In the absence of a written constitution, the checks and balances on executive action are ultimately political - and depend on politicians (and perhaps civil servants) acting individually or collectively to prevent or modify poor or reckless government decisions.

This check on the executive doesn't work for well-known reasons and can even be evaded by a ruthless Prime Minister and his or her cronies in power, as has been the case throughout my life-time (e.g., Attlee's secret decision to build the atom bomb, Eden's plot with Selwyn Lloyd to invade Egypt with the French and Israelis).

A halfway decent written constitution could in my view have prevented both Blair and Eden from pitching this country into damaging and immoral wars, as well as preventing many lesser, but serious, "policy disasters". Meanwhile, what about some humility? Let's not talk about "Great Offices of State" any more?