The 37-year-old star, who was known as Baby Spice, and her fellow bandmate, nicknamed Sporty Spice, dug out their old outfits from the 1990s to wear to their friends' event and despite being worried people would mock them for going as themselves, the blonde beauty admits they got a great reaction.
She exclusively told BANG Showbiz: ''Me and Mel C went to a fancy dress party recently and I went as Baby Spice and she went as Sporty Spice. We got all the old dresses out and it was hilarious!
''We thought about it and thought it would be fun but then when we were actually doing it we thought, 'What are we actually doing? We're going as ourselves!' But it actually worked out well.
''It was very funny and we took lots of pictures. It was really good fun.''
Emma - who has sons Beau, five, and Tate, two, with long-term partner Jade Jones - loves seeing her fellow bandmates but she was ''gutted'' recently when she was too ill to go out with Mel B and Mel C, and they kept jokingly mocking her by sending her videos from the dancefloor.
She added: ''I see Mel C all the time and I see Geri [Halliwell]. Mel B was over the other week and her and Mel C went out but I was so gutted because I was ill and one of the boys was ill so I couldn't go.
''They were sending me videos of them in the club going, 'Hey! We miss you!' I was thinking, 'Thanks.' It was just such a shame that I couldn't go out but I was unwell so never mind.''
Spencer Morrill believed he was in a relationship with the singer and that she was hiding messages for him in her songs.
Was the singer unknowingly taking counterfeit pain medication?
Roberts had left the band in 2012, due to problems with blood circulation and other health issues.
The popstar turned actress is back in the studio.