Illustration: David Foldvari

I have been too busy to see The Iron Lady (which I assumed was a distaff spin-off from Marvel's Iron Man), but none the less, I am now about to use it as a lead-in to discussing the critical rehabilitation of Margaret Thatcher. I did, however, find time to watch Troll Hunter last week, an enormous metaphor for Norwegian national identity, which engaged more critically with Norway's mythologised past than The Iron Lady does with ours. I expect. I haven't seen The Iron Lady, as I said.

Phyllida Lloyd's Thatcher biopic includes some daring sight gags employing the literal snatching of milk, but softens the controversial prime minister's legacy. The sympathetic figure of the ageing Maggie is played, by all accounts brilliantly, by the always excellent Glenn Close, her micro-managed Hollywood features magically transformed by hours of painstaking make-up into those of a normal-looking British woman. The old Thatcher remembers her career and divisive and unpalatable riots and strikes and wars acquire an inevitable multiplex gloss.

I have two similarly market-skewed biopics in production, both featuring Oscar-coveting actresses in disfiguring prosthetics, both factually tweaked to avoid punter alienation. In The Meat Man, the elderly Jesus (Meryl Streep) sits in Heaven remembering when lovely wise kings gave the young Jesus (Glenn Close) presents, his outrageous egalitarian teachings forgotten. In Der Fleischmensch, the elderly Hitler (Meryl Streep) sits in his Berlin bunker, recalling his struggles to be taken seriously as a young landscape artist (Glenn Close), the problematic Nazi years now merely light comic relief.

Conveniently, the appearance in the National Archives this month of secret Thatcher-era documents, revealing some surprising moments of sensitivity, has come at a good time for improving perceptions of the Iron Lady and the current Conservative party, both of which, despite undeniably strong performances from their charismatic leads, have suffered at the hands of critics, and are unlikely to spawn long-running franchises.

In the light of these documents, Thatcher has been praised for not agreeing to the "managed decline" of Liverpool, proposed by 80s colleagues. Here, we see the soft heart of Margaret the Woman, the tear-stained blouse of Maggie the Mum. I believe countries should be run like small businesses, and just as one would close down a loss-making shop or sack a sickly employee, so unprofitable towns and their unproductive citizens should be let go also. But Thatcher the maternal metal mother chose to view the feckless Liverpudlians somehow as legitimate stakeholders in their nation, deserving of the support of their own government, and she would not cast them out into the Wirral, to smelt stolen road signs, spit and form heroically self-regarding and influential neo-psychedelic groups.

There are many revelations in the released documents that appear with hindsight to show Thatcher implementing unambiguously brilliant and pragmatic strategies. Much has been made of how, despite the terrifying reality of their threats to her, she nevertheless "opened the back door for negotiations with the IRA" and initiated the peace process that Tony Blair took credit for. I went to the Public Record Office to scour the documents.

Oddly, the idea of opening the back door for negotiations with the IRA never appears in the body of any of the cabinet transcripts themselves, but only in the margins of Thatcher's personal parliamentary briefings. Here, the phrase "open the back door for negotiations with the IRA" is written in Thatcher's own hand, often underlined, or followed by mass exclamation marks, as if to remind the femme ferrous that she must follow up the idea later. And yet there never seems to be any obvious relationship between the idea of opening the back door for negotiations with the IRA and the content of the printed texts the handwritten recommendations append.

I checked the dates. Thatcher writes "open the back door for negotiations with the IRA" on documents dated 31 March 1982, 2 May 1982, 9 February 1985, 3 March 1985, 19 July 1987, 24 May 1988, and every 10 May, or the Friday nearest to it, throughout. On the first six dates, respectively, terrorist Nelson Mandela was moved out of sight to Pollsmoor prison; the Argentinian warship the General Belgrano was torpedoed outside the Falklands exclusion zone with the loss of 323 lives; Russ Abbott's haunting pop single "Atmosphere" peaked at number 7 in the UK chart; the miners' strike ended; Nick Faldo claimed victory in the Open; and the anti-gay Section 28 legislation was passed. All these events would have been causes for celebration either for Margaret Thatcher herself (Russ Abbott fan), for her husband Denis (left-handed golfer) or for both Thatchers (known rightwingers).

The significance of 10 May was more confusing, until good old Wikipedia revealed it to be the date of Denis Thatcher's birthday. Despite the attempts of oxymoronic contemporary Tory feminists to appropriate her, Margaret Thatcher was a traditionally dutiful and obedient wife. Was "opening the back door for negotiations with the IRA" a code for some kind of treat for Denis, who attended a nonconformist public school, or did it really refer to clandestine attempts to lubricate republican relations? And did it explain Thatcher's intermittently unusual walk, which her biographer, Charles Moore, famously described as a "dignified scuttle"?

The implication that these "back-door negotiations with the IRA" occurred on days of celebration for the two happy Thatchers, humanises Maggie in a way that Glenn Close's, admittedly uncannily accurate, impersonation of the woman simply does not. Lloyd draws a discreet sheet over Thatcher's back-door negotiations and concentrates instead on visual puns about milk. Sadly, in hindsight, Lloyd must realise that The Iron Lady would surely have earned more than its usual two- or three-star reviews if only she and Glenn Close had shown the courage to bring Thatcher's back-door negotiations to the silver screen in detail, perhaps in 3D. But in preserving untarnished the cast-iron enigma of Margaret Thatcher, this stainless-steel sister, this un-fatigued metal maiden, Lloyd ensures the legend of this particular Iron Lady will never rust.