Geri Halliwell says she was holding back the tears when she watched the workshops of the new musical.
Mel C added that the rehearsals gave the girls "goosebumps" and it was a "lovely thing"
The girls said the musical supports Girl Power's longevity. "Who would have thought the message is still standing 16 years later".
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The prime minister said "tough new rules" will be introduced to tackle the behaviour of executives who put their workers' pensions at risk.
The musician, whose career spanned six decades and included 18 years with The Kinks, died on Saturday after a fall.
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