They were even caught on camera dancing and singing along to Spice Girls hit Say You'll Be There.
Beckham said: "Fun night celebrating @realgerihalliwell... I love you all!"
The fashion designer also shared a picture of her and her former bandmates with their partners - David Beckham, Jade Jones and Christian Horner.
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TV presenter Rylan said he had had the "best night" and joked he looked like a competition winner as she shared a picture of himself with the singers and video footage of them dancing to their hit.
Mel B, 47, was conspicuous by her absence from the party.
Watch: 'We drank so much!' Emma Bunton reveals party life of the Spice Girls in the 1990s
She has just given an exclusive interview to Hello magazine, confirming her engagement to Rory McPhee.
She shared a link on social media to the magazine photoshoot, and a throwback picture of herself with Spice Girls Beckham, Bunton and Mel C, but not Horner.
There have been rumours of a feud between Ginger and Scary Spice after Mel B claimed the pair slept together back in the 1990s.
Mel B confessed to the brief intimacy while filming an episode of Piers Morgan’s Life Stories back in March. The Two Become One singer was there to promote her new book ‘Brutally Honest’ before she touched on the pals’ romantic past.
Horner denied the story.
Mel B told Hello magazine of her new engagement: "For the first time in my life, I'm engaged to a beautiful, honest person who makes me feel protected, nurtured and so loved, and I want to savour that."
Speaking about her fellow Spice Girls' reaction she said: "Emma [Bunton] cried, so did Mel C."
This will be Mel B's third marriage, having previously been wedded to Jimmy Gulzar from 1998 to 2000, and Stephen Belafonte from 2007 to 2017.
She has three daughters, Phoenix Chi, 23 from her marriage to Gulzar; Angel Iris, 15, from a relationship with actor Eddie Murphy; and 10-year-old Madison from her marriage to Belafonte.
Mel B has spoken publicly of physical and mental abuse she suffered during her relationship with Belafonte.
While headline acts for the festival have not yet been confirmed, rumours are abound that the Say You'll Be There singers will be on the bill.
But Beckham told US show Watch What Happens Live with Andy Cohen: “I had so much fun being in the Spice Girls.
“But now, with everything else that I have got going on with my fashion and my beauty line, four children, I couldn’t commit to that.
"I love the girls. I really, really enjoy singing Spice Girls when I’m doing karaoke, but I think I’d better leave it there.”