This is actually kind of old now but couldn't see it had been posted previously...
On 22nd July 2013, BPI (The British Music Industry) updated their database to update 1,000s of certifications and there were a few Green Day awards updated:
Singles - The following were all certified Silver (for sales of 200,000):
Basket Case
Good Riddance
American Idiot
Boulevard of Broken Dreams
Wake Me Up When September Ends
Albums:
1,039 Smoothed Out Slappy Hours - certified Gold (100,000 copies)
Kerplunk - certified Gold (100,000 copies)
Shenanigans - certified silver (60,000 copies)
International Superhits - certified 2 x Platinum (600,000 copies). This also gives Green Day their 3rd multi-Platinum album in the UK after Dookie (3x Platinum) and American Idiot (6x Platinum)
DVD/Video:
International Supervideos - certified Platinum (50,000 copies)
Sorry if it's already been posted but couldn't find it and thought it was pretty interesting.