I've been watching, again and again, TV clips of Margaret Thatcher going into her old home, 10 Downing Street, today on the arm of her latest successor, Gordon Brown. She may be frail at 81, but her political legacy remains as tough as steel, appropriately enough for the Iron Lady, as she was. I wonder if the former Tory leader realizes what a favor she's doing for Brown. I suspect she does, but that she also is happy, Labour Party leader though he may be, to bask in the admiration of the man called the Iron Chancellor before he became prime minister in June.

Brown needs Thatcher. Long suspected of being further to the left than his predecessor, Tony Blair, Brown has spent all summer nailing his feet down to the center of the political spectrum -- from taking a hard line on terrorism to proposing English language test for new immigrants to Britain. He's been brilliant at staking out positions that lie well within the natural ideological territory of the Conservative leader, David Cameron. Cameron, for better or worse, has been moving his party to the left as he attempts to modernize it and prepare it for the next general election, sometime before the summer of 2010.

And Thatcher needs Brown. She's long told friends that her last great political accomplishment was the Blair-led reform of the Labour Party. Blair embraced much of what Thatcher stood for in the economic sphere. It's no accident that the last time she visited Number 10 she did so at Blair's invitation seven years ago. So, in the winter of her life, for Brown to show her the respect Blair did further burnishes her legacy, one of the sturdiest political inheritances of postwar Britain.