The movie, a spinoff from E4's popular sitcom, has outpaced Hollywood rival Cowboys & Aliens with a £2,584,106 opening haul. Inbetweeners is on course to secure the weekend box office top spot ahead of the Daniel Craig Western/sci-fi mash-up and Glee: The 3D Concert Movie.
Showings across the UK's 409 sites are reportedly selling out fast, prompting Entertainment Film Distributors to look for more screens to host the teen comedy movie.
The Inbetweeners Movie follows Will (Simon Bird), Simon (Joe Thomas), Jay (James Buckley) and Neil (Blake Harrison) as they finish their final year at school and head out on a lads' holiday to Malia.
"We are all delighted by the response to Jay, Neil, Simon and Will's summer holiday," said producer Chris Young. "We've been so excited for people to see the boys on the big screen and we are thrilled that the UK feels the same!"
Inbetweeners co-creator Damon Beesley told Digital Spy that the movie may be the last chance to see the quartet together on screen.
He said: "The Inbetweeners itself has always been about a time in your life between when you're a school kid and before you go to university, you're sort of a full-fledged adult for the first time. It's that phase in between.
"Unless you squeezed a lot into that three months of their lives before they went to university there isn't really a lot of scope to continue that so it does feel, very sadly, like this is the end of The Inbetweeners."
More Inbetweeners Movie coverage:
> The Inbetweeners Movie premiere - in pictures
> Inbetweeners interview: Simon Bird, Joe Thomas, James Buckley, Blake Harrison
> Inbetweeners Movie interview: Iain Morris, Damon Beesley
> Video: Inbetweeners stars answer questions... from a beaver
> The Sims parody The Inbetweeners Movie - video
> The Inbetweeners Movie review