Simon Cowell is planning a lavish £250,000 party for his 50th birthday.

The music mogul has invited 400 celebrity friends to help him celebrate reaching the landmark age with an exclusive black-tie bash at Hertfordshire's Wrotham Park on October 7.

A source told Britain's Daily Mirror newspaper: "Simon's been planning this party for months and the guest list is phenomenal - a 'Who's Who' of the celebrity world.

"It's going to be the highlight of the showbiz calendar. Simon's not a massive party person, so when he says he's going to do something, he does it in style."

Guests expected to attend include music legend Sir Elton John and his partner David Furnish, Hollywood actor Kevin Spacey, actress Denise Richards, supermodel Kate Moss, Australian pop star Kylie Minogue, the judges from his talent shows and most of his recording artists.

Simon's 'American Idol' make-up artist Mezhgan Hussainy - who he is reportedly dating - has also been invited to the October party along with his ex-girlfriends Terri Seymour, Jackie St Clair and singer Sinitta.

The bash will be hosted by Simon's record label Sony BMG and some of the world's biggest acts - including 'X Factor' winner Leona Lewis, Il Divo and Westlife - will perform for the star-studded guests.

The source added: "All his recording artists have been invited. And all the judges on his shows from both sides of the Atlantic.

"He's always incredibly composed but he'll definitely be toasting his birthday properly. There will be champagne on tap, plus a three-course banquet.

"But he can't get up to too much, as his mother Julie is the guest of honour."

In July, Simon was treated to a surprise early birthday bash, hosted by his long-time friend Jackie.

Following the party, Simon said: "It was supposed to be a quiet affair, so it was all a big surprise. Carly Simon did say that she wrote 'You're So Vain' about me, which was highly amusing. It was a great night."