Half-century, not out. Cherie marks her 50th at Chequers

It has been billed as a "small, private affair" but Cherie Blair's 50th birthday party this evening is seen as one of the most exclusive and sought-after invites in the political calendar.

It has been billed as a "small, private affair" but Cherie Blair's 50th birthday party this evening is seen as one of the most exclusive and sought-after invites in the political calendar.

The celebration, for about 80 of Mrs Blair's closest friends, will be held at Chequers, the Prime Minister's country residence in Berkshire, in one of its grand state rooms.

The former glamour model Carole Caplin, Mrs Blair's "lifestyle guru", is said to be on the guest list, as is Lord Falconer and his barrister wife, Marianna Hildyard, close friends of the Blairs for more than 20 years. Sir Cliff Richard, whose house in Barbados has been used by the Blairs for family holidays, was invited but cannot attend.

The party, which is being catered with enough champagne, wine and food for up to 100 people, will be held in the grand Elizabethan residence set in 1,200 acres of farmland and woods near the Chiltern Hills.

Yesterday, a friend of Mrs Blair said the party would be a "totally private event for close friends and family, with no glitz".

The Blairs will pay for it themselves, and even close allies of the Prime Minister, including Alan Milburn, newly restored to the Cabinet, and Margaret Hodge, are expected not to attend.

But at Westminster yesterday, the the invitation list was regarded as a litmus test of who was "in" and who was "out" of the Blair political circle.

Lord Irvine, the former lord chancellor, who was Cherie Blair's pupil master when she was a trainee barrister, is invited, even though he is said to have fallen out of favour with the Prime Minister over his proposals for judicial reform

But Fiona Millar, who for years closely protected Mrs Blair as her aide and adviser at Downing Street, does not feature on the guest list, and nor does her partner, Alastair Campbell, former director of communications at Number 10.

Neither is Anji Hunter, who used to run Tony Blair's office, and for years was his closest aide. In the words of Anthony Seldon, the Prime Minister's biographer, she was the person he "relied on ... for emotional and psychological support".

Mrs Blair is said to have a fraught relationship with Ms Hunter, a super-confident figure from an upper-class background. Peter Mandelson, who is also not believed to be among Mrs Blair's favourites, is not understood to be on the guest list. And nor is Gordon Brown, whom Mrs Blair is said to despise.

Even Mrs Blair's discreet Downing Street "gate-keepers" Jo Gibbons and Hilary Coffman, who fend off the prying media, are not thought to be attending. "This isn't a political party, it's a private do. You wouldn't recognise a lot of the names on the guest list," said one insider.

Many of the cars that draw up to the grand Berkshire residence tomorrow night will belong not to the members of the great and the good, but to old friends of the Blairs.

Former flatmates, next-door neighbours and colleagues she met at the start of her career will be sipping champagne and toasting Cherie, along with her children and family members. There are likely to be speeches, as at Cherie Blair's 40th birthday party 10 years ago where she touchingly declared about her husband that she "loved him".Cherie Blair is known as a fiercely loyal person who values and nurtures not just her family, but her friendships as well. Her position as politics' First Lady has not seen her abandon old friends for flashy new ones. Pals she met at the London School of Economics, where she took a first in law, are still in her circle, as are her colleagues as an up-and- coming barrister.

Among those invited tonight are Maggie Rae, a solicitor who the young Cherie Booth shared a flat with in London before she married Tony Blair. The two women remain close friends.

Her husband, Alan Howarth, who was secretary of the Parliamentary Labour Party until being enobled by Tony Blair as a Labour peer, is also said to have received an invitation in the post.

The millionaire television producer Barry Cox, who lived next door to the Blairs when they lived at their first house in Mapledene Road, Hackney, is also on the invitation list. Mr Cox, who worked on the This Week programme with Jonathan Dimbleby and David Elstein, later moved to LWT, later climbing the executive tree to become deputy chairman of Channel 4. The Blairs used to nip next door for drinks with Mr Cox and his then wife Katie Kay (who is also believed to be invited), and the two couples also holidayed together at Mr Cox's house in France.

Mrs Blair's close friend, the solicitorVal Davies, who sprung to her defence when it seemed a former nanny was considering publishing compromising details about the Blairs, is also expected to be invited.

Martha Green, an American friend who runs a leading restaurant in the West End, will be at the party. Ms Green, who used to work in advertising, has become unofficial caterer "to the court of Tony Blair".

Members of Mrs Blair's extended family - including her mother Gale Smith, who still babysits for Leo in Downing Street - and her full sister Lyndsey will be there.

But none of Cherie's five half-sisters, by her father the actor Tony Booth, are thought to be on the guest list. They include Lauren Booth, who makes a tidy living as a commentator and columnist.

The seemingly inauspicious date of September 11 is not Mrs Blair's actual birthday, which falls on September 23. But it is said to be the only date when all of Mrs Blair's children - including Euan, who is at Bristol university, and Nicky who is starting at Oxford, where he will read history - will be available to attend.

Next week her first book, The Goldfish Bowl, about spouses in Number 10, will be published. The book was co-written with Cate Haste - who is expected to be at the party with her husband Melvyn Bragg, the broadcaster writer and Labour peer.