If you're not from the UK, you'll need to use a manual proxy like:
126.96.36.199 with port 80
(Before you set the proxy you might need to clear you browser history! More on how to use a manual proxy click here!)
Join the club if you're not already a member.
Scroll down and enter following code to unlock the interior: 3607342152748
and click 'Unlock'.
When you go to your suite and open the box you'll get a message saying the interior is unlocked and can be found under 'Room Design'.
V. thanks to LISAKARA2000 and Browse in Stardoll