Prometheus is CONFIRMED a 15 cert in the UK. Bearing in mind thats probably what the original Alien would rate these days I'm pretty happy with that. It will be as Sir RS has intended without any cuts. Also intersting is this;
"In the United Kingdom the film will be officially released on June 1, 2012 and will open in IMAX with midnight screenings beginning May 31, 2012. 18,827 tickets were pre-sold for the London IMAX, the largest IMAX screen in the country, breaking the theater records for the highest grossing week of pre-sales with £293,312 ($474,687), and the highest grossing first day of pre-sales with £137,000 ($221,717), exceeding the performance of other high-profile IMAX releases including The Dark Knight and Avatar."
Guess theres a lot of Alien fans out there!