Hundreds of fans have been camping out since Sunday, with posters and banners at the ready.
For those who can't make it down to London, fans can watch the action live from 5:30pm GMT with HELLO! Online, from the moment the famous five arrive on the red carpet to, no doubt, deafening cheers and screams.
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The pop sensations are just as excited as their fans are for the UK premiere and have kept their Directioners updated on Twitter.
"Just pinching myself! Absolutely huge day today! We want u to know that u made this all happen! And when u see the film or are standing on Leicester square tonight! U can all turn to each other and be like "we did this" so thank you so much," tweeted Niall.
"Long day of interviews for the film.. Got me excited for tomorrow," posted Harry.
Liam took the opportunity to praise their famously devoted fans, saying, "We all think our fans are amazing. The dedication they show is second to none and we think they're the best fans in the world."
"I think it's a way for us to get across what we're like and what we're like with each other," said Harry.