Geri Horner knows just how to unite a nation - from an upcoming stadium tour with her Spice Girl bandmates, to playing head judge on Saturday night hit All Together Now. And it all stems from having fun, she tells Gemma Dunn...

When the Spice Girls announced their tour last November, fans rejoiced.

The long-awaited reunion will see pop icons Geri Horner (nee Halliwell), Melanie Chisholm, Melanie Brown and Emma Bunton embark on a huge stadium tour - their first in more than a decade and their most exciting revival yet.

"Bringing girl power and our message of friendship and love back to the stage feels more relevant than ever," said the bandmates, when news broke of their comeback. "We hope everyone can join us for one big Spice Girls party."

True to form, Girl Power took hold. And with hundreds of thousands of tickets sold - despite Victoria Beckham opting not to take part - extra dates were added to meet demand.

Now, with just months to go, tension is mounting.

"People keep saying, 'Are you excited?'" Horner, 46, says, when we meet in January. "But before you get to the excitement - and it is exciting - there's so much to organise that you've got to get through that!

"We've started casting the dancers," she offers.

"The problem with me is, I'm not very discreet, I've got a terrible poker face..." she adds with a laugh. "But it's been amazing. We've picked a really good squad of people."

Talking at the season two launch of All Together Now, Horner, aka 'Ginger Spice', is certainly keeping busy.

The hit BBC One entertainment show, headed up by the bubbly pop icon along with comedian Rob Beckett, is back. This series will welcome a whole new range of performers to the stage to sing in front of The 100 - a unique panel of music experts and singers from all over the UK.

Need reminding of the rules?

If any of The 100 like what they hear (expect to see show favourites Divina De Campo, Paulus and Mr Fabulous, as well as new recruits), they can stand up, and sing along.

The greater the number that join in, the higher the act's score. And at the end of the series, one act will walk away with a staggering cash prize of £50,000.

Life-altering, yes, but the Saturday night's biggest sell is its feel-good factor, insists Horner.

"It works because it's the perfect antidote to modern living," says the Watford-born star, who will return to impart her judgement as head of The 100.

"We live really stressful, fast-paced lives. And what we love about All Together Now is it does what it says on the tin.

"When you turn it on, you feel safe, and you know that you're going to feel good," she elaborates. "It lifts you up to a place that's well-needed."

"It's also a show for everybody," she acknowledges, "because if you look at The 100, there is someone that is you in there. We've got every walk of life, every age, every background.

"You can find your person that reflects your opinion."

Now more than ever we should embrace that feeling of togetherness, advises the mother of two.

"I can only go from my experience, but when the Spice Girls performed at the Olympics at London 2012, we had a little slot of three and a half minutes to unite the world - and you can do that with music," says Horner.

"All Together Now (which has sold its format to 12 markets in just 12 months) just really shows that we're all different, and actually we can all sing along and just have a laugh with it.

"It reminds us that we're all fundamentally human beings, and we can get along," she concludes.

Marking herself down as an honest and fair critic ("We don't want to take anyone down"), Horner has certainly earned her judging stripes on Popstars: The Rivals, The X Factor and Australia's Got Talent.

Though this time around, she's reviewed her technique.

"On this series, I just thought, 'This is £50,000 and every 'yes' is a 'no' to somebody else', so I decided to raise my bar a little bit," she explains.

"Somebody has to be the leveller, the reality check, the feet on the ground about it, in a really conscious way.

"This is fun, but it could change somebody's life," she states, referencing last year's winner, Michael Rice, who will represent the UK at the Eurovision Song Contest 2019.

"I wanted to respect the whole premise of what this is about," she says. "I care about telling the truth more than whether you love me back."

But while the hit maker knows exactly what it takes to get a crowd on its feet, she's the first to admit she wouldn't put herself before The 100.

"A normal performance, you go out and the majority of the time, it's dark and British people are very polite - they'll clap anyway," says Horner.

"But this is instance," she reasons. "Can you imagine - you're singing there, and nobody's standing up? I'd be like, 'Okay... I'm going!'"

How does strutting her stuff with the Spice Girls compare?

"I tell you, it is easier," she says. "When you harmonise with somebody, first of all it can help you keep in tune. It's like someone holding your hand through something and it makes you sound better too."

"I performed both as an artist, solo and collectively," she continues. "They both have their cross to bear, but the benefit is, it's just more fun if you're enjoying it with other people."

Going forward, Horner just wants to be happy, whatever she turns her hand to.

"Sometimes we have the gift of choice in our lives, of which projects we're going to choose to do, and what I've learned now - and I'm 46 years old - is the most precious thing we can give each other is our time," she shares.

"We've got no guarantees how long we're going to be on this planet for, and I'm a mum, I love being at home with my children.

"But actually, if I'm going to give myself to something, I want it to be worth it and I just feel like All Together Now is so worth it."

All Together Now returns to BBC One on Saturday.