Downing Street has a new Iron Lady – only, this time, Maggie lives at No 11

Michelle Obama called Maggie Darling a 'Scottish firebrand', and she's just the latest Treasury matriarch to prove a real asset

Joining her husband on the steps of 11 Downing Street on Wednesday, as he held aloft his Budget box for possibly the last time, Maggie Darling leant her head shyly on his shoulder in a rather touching public display of affection.

But the real Mrs Darling is far from shy and retiring. She is, like another Maggie, an Iron Lady, and one whose grit and determination were instrumental in the Chancellor's firm stance against Gordon Brown in unveiling a "keep calm" plan for the public finances.

The Prime Minister wanted what could be his government's final Budget to be sweetened for the electorate, using extra billions from lower borrowing and higher tax receipts for vote-winning giveaways.

But Mr Darling's allies made clear it was "Alistair's Budget", and in the end there were few gifts for voters for fear of upsetting the markets. The Chancellor may be under fire for failing to come clean on the extent of cuts across Whitehall, but there has been little effect, so far, on the polls.

Mrs Darling was key to urging the Chancellor to remain firm against Mr Brown over the Budget, as she has been at every crucial stage of their nearly three years in No 11. Maggie Darling's name is now the stuff of Westminster legend after she featured last month in Andrew Rawnsley's book on the fall of New Labour.

When leaks from No 10 claimed Mr Darling was facing the sack last year, Mrs Darling is reported to have raged: "The fucking cunts are trying to stitch up Alistair! The cunts! I can't believe they're such cunts!" – although it emerged later the word she actually used was "bastards".

Michelle Obama, after meeting the former journalist a year ago, described her as a "true Scottish firebrand". As Maggie Vaughan, she was a journalist for the Daily Record and Glasgow Herald, and remains well liked among politicians and journalists.

At the same Downing Street reception where she impressed the US First Lady, she was the heart and soul of the party, introducing Dame Kelly Holmes to Mrs Obama and other leading female figures. But she is not the first chancellor's wife to have a reputation for feisty loyalty to her husband.

Elspeth, now Lady, Howe typifies the formidable political spouse. When her husband Geoffrey was appointed Chancellor by Margaret Thatcher after the 1979 election, she was already a success in her own right. But that year she was removed from her post as deputy director of the Equal Opportunities Commission by the new Prime Minister. It is perhaps no surprise that Lady Howe became a critic of her husband's boss: she is assumed to have helped to write Lord Howe's devastating resignation speech of November 1990, which played a pivotal role in bringing down Lady Thatcher.

Denis Healey, while he was Labour Chancellor, described an attack by Lord Howe (at that time his Tory shadow) as like being "savaged by a dead sheep". Months before her husband's demolition of Lady Thatcher, Lady Howe remarked portentously: "Beware the wolf in dead sheep's clothing."

Lord Healey's wife, Edna, was a successful biographer while her husband served in the Cabinet for 12 years. Her books, including her autobiography describing the life of a political spouse – Part of the Pattern: Memoirs of a Wife at Westminster – drew similar conclusions: that powerful men marry strong, determined women.

What of Mrs Darling's successors? If the Conservatives win, the No 11 parties will be hosted by Frances Osborne, the author wife of George Osborne who has been described by friends as a "feisty feminist". Last week, Vince Cable, the Liberal Democrat Treasury spokesman, said he was "ready to serve" as Chancellor in the event of a hung parliament. If so, his wife, Rachel Wenban Smith, will be picking out the curtains at No 11. A New Forest farmer, her first encounter with Mr Cable involved a heated argument about Liberal Democrat policy on free trade.

If Labour pulls off a shock victory, then there will be a power struggle between Ed Balls, Mr Brown's closest political ally, and Mr Darling for the job. Mr Brown said yesterday that the incumbent would "of course" remain Chancellor. Mr Balls's wife, Yvette Cooper, is already a cabinet minister and is unlikely to assume the role of No 11 chatelaine.

But if Mr Brown keeps his word, and if Labour does win or forms a government in a hung parliament, Maggie Darling will remain a fixture in our lives for some time to come.