Matthew Norman: The perfect New Labour scandal

Never has an opposition leader had better reason to sing as he cycles to work than David Cameron has today. His only conundrum is which song. In honour of the £1m property tax masterstroke with which the Liberal Democrats have handed him a clutch of London and South West marginals, he might be tempted by "Vincent". "How you suffered for your sanity/ How you tried to set them free" as Don McLean has it. "Perhaps they'll listen now."

Well, they have listened now, Vince Cable's colleagues, and wisely decided it's the opposite of sanity to cane someone who paid £32,000 for a four-bed Richmond semi in 1981. Alternatively, contemplating Mr Clegg's Light Brigade charge onto Cameron ground with his doolally talk about slashing public spending, he could go for the Billy Cotton's big band number "Oh Nicholas Don't Be So Ridiculous".

The favourite, though, must be the celtic ballad, which begins "Bonnie Scotland, I adore thee!", because the boon granted him by the Attorney General can scarcely be measured.

The tale of Patricia Scotland and her Tongan illegal so neatly encapsulates so many of New Labour's least enchanting traits (arrogance, incompetence, lust for needlessly intrusive law, venality, reliance on whitewashing, the smugness and exhaustion of those in power too long, and, above all, startlingly brazen hypocrisy) that it has the flavour of a crude satirical conceit. It is also an indecently perfect morality play about the dangers of the centre left hopping into bed with right wing tabloids. Invariably, they emerge with a discharge and itchy rash.

Lady Scotland picked up her dose by enacting the law obliging employers not only to check the documentation of non-EU workers, but also keep copies. From a government that nudge-nudgingly, wink-winkishly encouraged an illegal immigrant workforce as cheap fuel for an overheating economy, such legislation could have only one intent: to assuage The Sun and Daily Mail, the latter being the title that grassed her up and allowed her to become the first private citizen to be fined for breaching it.

When she took up her post, Lady Scotland had a dig at her predecessor's abrogation of duty over Iraq, adding to the oath of office a line about respecting the rule of law. Nothing wrong there. You'd want that spelt out to a law officer, wouldn't you? "We had to make sure the public better understood that the attorney was there", she said last December. "To make sure that the rule of law was present right at the heart of government." Aha.

With hindsight, she probably should have added: "Unless it's a footling civil offence on a par with not paying the congestion charge." And she needs plenty of that, what with lacking the foresight of others who warned that the 2006 Immigration, Asylum and Nationality Act she steered through the Lords would, to quote The Daily Telegraph at the time, "unfairly prosecute small businesses hoodwinked by illegal immigrants with sophisticated forgeries of passports or other documents." But no, no, no, ministers know best, and this one dismissed the warnings with a disdainful "meh".

So much for the hypocrisy and venality of passing law to persecute those, like her maid, who pay every farthing in tax and national insurance owed, while herself receiving £170,000 in housing expenses to which she appears wholly unentitled. As for the incompetence, even assuming Lady Scotland tells the truth about being shown sophisticated forgeries, failing to keep photocopies must be an automatic sacking offence. Even the most supple-minded of sophists couldn't manufacture a counter-argument to this. It doesn't speak for itself. It screams until the eardrums beg for mercy that when the country's senior law officer breaks a law she helped enact – and one deliberately framed to clarify that ignorance to it could be no defence – she must go, and go at once.

And so to the amalgam of fatigue, whitewash and complacency that allows her to stay. No one would expect this government and its apparat to respect the precepts of natural justice themselves, so one can hardly fake astonishment that cabinet secretary Gus O'Donnell – a man with larger stocks of gleaming white paint than Dulux – cleared her of breaching the ministerial code in half the time it takes Usain Bolt to run downstairs.

Although the maid had scarpered before the immigration thugs smashed down her front door for the benefit of attendant press photographers, it would have been nice had Sir Gus waited for her capture and affected to listen to her version before coming to his judgment. Purely for appearance's sake. After all, this poor, frightened woman has been accused of forging official documents. So by acquitting Lady Scotland solely on her own evidence, Sir Gus implicitly convicts the maid of an imprisonable offence.

The arrogance inherent in this is surpassed only by the sheer exhaustion that explains her ladyship's survival. Gordon Brown cannot have been unaware for a moment that keeping her is a colossal political mistake.

With the expenses furore finally fading from the forefront of public consciousness, her retention reignites the rage over this curious two-tier system that indemnifies only those who pass the laws and rules they break. Unless Sarah Brown has a phalanx of Marigolds-clad Filipinas chained to the No 10 basement walls, the only plausible explanation is that, what with finding trophy cabinet space for his World Statesman of the Year award, he no longer has the energy for domestic trivia of the kind.

In a Britain sorely in need of non-white political role models, it is a shame that this one has proved a disaster, and a real sadness that someone who was raised in Walthamstow as one of 12 children of immigrant parents would enact a horrid little law designed to punish others coming here, much as her parents did, to better their lives through hard work. The schadenfreude provided by watching it come back and bite her on the bum is small consolation for that.

But it is as an unwitting, yet richly talented, seamstress that I will remember Patricia Scotland. In knitting together the myriad of flaws that will soon drive Labour from office, Baroness Scotland has produced nothing less than the Bayeux Tapestry of her party's demise.