Prime minister's questions sketch
By Nick Assinder
Political correspondent, BBC News website
I'm not sure what the penalty for openly challenging the Speaker of the Commons is - hung from the ancient rafters in Westminster Hall by the ears while being pelted with old volumes of Hansard I suspect.
Whatever it is, Tory leader David Cameron - and quite a few MPs - were so incensed by his latest gagging order they came as close to it as anyone can remember for decades.
Mr Cameron and others were overcome with indignation when Speaker Michael Martin interrupted him as he attempted to ask the prime minister if he still supported Gordon Brown as his "successor".
In an extraordinary ruling, Mr Martin declared the prime minister does not have to answer such questions, he is in the Commons to talk about government business not who will be the next leader of the Labour Party - that is party political business.
So here was a bit of history being written on the Commons equivalent of tablets of stone. And it puzzled and angered many who felt it looked like an attempt to protect the prime minister.
There was a nano second's shocked silence as the full import of this official ruling - and they don't get more official than this - sank in. Particularly as Mr Cameron had never mentioned the Labour leadership and may well have been asking about Mr Blair's successor as prime minister.
The Commons chamber erupted and the leader of her majesty's official opposition started down what might have turned into a very risky route.
"Are you honestly saying we cannot ask the prime minister...." he began before being cut short.
There were some sharp breaths at this challenge to
the referee (although that label hardly does justice to the office of Speaker).
Everything that comes from this Chair, glowered Speaker Martin, is said in honesty. The ruling has been made.
Cameron started to challenge ruling
There were no threats, but there didn't need to be. Mr Cameron could probably feel the chains sliding around his wrists - but he went on to prove he could think on his feet and found a way around the apparent gagging order.
He asked Mr Blair who he would like to see as the next prime minister.
"I will allow that, that is in order," declared the Speaker.
It wasn't just Mr Cameron who received a red card from Speaker Martin.
The prime minister has previously been ticked off for trying to quiz the Tory leader about his policies - and he even had to check with the Speaker that he wasn't over stepping the mark again this week.
Apart from this extraordinary spat, however, there were a couple of genuine developments.
The prime minister did, eventually, give an endorsement of sorts to Gordon Brown, saying he'd rather have him as prime minister than a man who had advised Tory Chancellor Norman Lamont on Black Wednesday, as Mr Cameron had done.
And, in answer to a question from Liberal Democrat leader Sir Menzies Campbell on Iraq, he also confirmed he was not ruling out another inquiry at some point in the future.
But it will be Speaker Martin's little bit of history making that will be remembered most by regular watchers of these sessions.
Will it have denied Mr Cameron one of his most effective weapons, or is the opposition leader - as most expect - nimble-footed enough to find ways around it?