Brexit is having an electrifying effect on Parliament. The Attorney General, Geoffrey Cox, was by turns trenchant, melodramatic, defiant, humorous, self-important, self-deprecating, penetrating, rueful and unyielding as he upheld the Government’s deal.

His rich, deep, sonorous, well-modulated voice makes him sound like one of the great actor managers of Edwardian times, appealing to his listeners’ emotions and love of spectacle as well as to their understanding. Here is a performer who projects what he wants to say as if he were still in the pre-microphone age, which in many of the courts where he appeared as an advocate was perhaps the case.

Like a stag at bay, the Attorney refused to comply with a Commons motion requiring him to release the legal advice he has given the Government on its Brexit deal, insisting over and over again that to so would not be in “the national interest”, words to which he imparted a tremulous note of pathos. Only a man deficient in any sense of honour, he implied, would so betray his country as to publish advice which could hinder our negotiators.

But Cox sought to temper his defiance, and render it acceptable to MPs, by answering “with uncompromising and rigorous fidelity” their questions, and by promising to be as straight with them as he is with ministers. He said that in the end, the question of whether or not to accept the deal is not one of “lawfulness” but of “prudence”.

Nick Thomas-Symonds, from the Labour front bench, accused him of showing “contempt” for Parliament. The Attorney replied that all Thomas-Symonds has to do, on any legal question about Brexit, is “to ask and he will receive”. Here the cadence was biblical.

Cox agreed there is no unilateral right to terminate the Northern Ireland backstop, admitted he would have preferred to see such a right included in the deal, but contended that the European Union would have no motive to remain in the backstop “indefinitely”, and would, indeed, find it even more irksome than the United Kingdom did, and “highly vulnerable to legal challenge”, so would be even keener to bring it to an end.

In other words, the backstop “represents a sensible compromise”. How fervently David Lidington, Theresa May’s right-hand man in Downing Street, nodded as he said those words.

Nigel Dodds, for the Democratic Unionists, refused to be persuaded by Cox’s “deeply unattractive, unsatisfactory presentation”. Cox replied that he had himself “wrestled with the question because I am a Unionist”, but had decided the backstop was “as much an instrument of pain” to the EU as to the UK.

Harriet Harman, from the Labour backbenches, told him the Government could not “openly defy the will of the House”. Cox replied: “I am caught in an acute clash of constitutional principle.” So he did not pretend the arguments were all on his side, but said that as Attorney General he could not act “regardless of the harm to the public interest”.

Jacob Rees-Mogg said it was not for the Government to judge whether or not to release papers which the Commons had demanded. Cox wondered where this doctrine ended. Did it extend to the papers of the Secret Service?

Turning to the Opposition benches, the Attorney said they could bay and shout, but it was time for them to grow up and get real, for the public interest was at stake.

When they shouted at him that he was being “arrogant”, he replied that on the contrary, he wished he could comply with the request of the House, but he simply couldn’t. By this stage one almost felt one was listening to Martin Luther saying “I can do no other”.

He added that “on all points of law I have given…my starkest judgment about what the situation truly is”, and repeated that in his opinion, the backstop will not last indefinitely. For all his histrionics, Cox sounded deeply sincere, in a manner politicians very seldom achieve when they are defending prudence, moderation and compromise.

I apologise for being so slow to file this report. It is hard to tear oneself away from listening to Cox, and hard also to give any proper idea of his forcefulness. I have never heard a more majestic counterblast to all those who think the Government’s proposed deal is a sellout.