Rowling discovered after the books were published that she had confused the layout of King's Cross with that of Euston Station, and that platforms 9 and 10 at King's Cross were not the ones between which she had meant her magical platform to be placed. There is no platform between tracks 9 and 10 at King's Cross. To solve this, the filmmakers re-numbered platforms 4 and 5 for the duration of filming. In reality, at both King's Cross and Euston, platforms 9 and 10 are separated by train tracks. The exterior shots in the film are that of nearby St. Pancras station.
Perhaps coincidentally, a local legend claims that Queen Boudica fought her last battle near the site of King's Cross Station, and her body is said to be buried somewhere between platforms nine and ten.
Today, King's Cross Station still has no Platform 9¾, but it does have a ‘Platform 9a’ and a ‘Platform 9b’. The secondary building containing platforms 9 to 11 has been decorated with a cast iron ‘Platform 9¾’ sign, complete with a luggage trolley ‘stuck’ halfway through the wall as tribute to the book. A wrought iron 'Platform 9¾' gate used as part of the film set is preserved at the National Railway Museum.