how do you get biro off painted doors

[metired]

my 2 youngest dd's and there 2 friends have decided to autograph their bedroom door with biro and bright orange felt pen, have managed to lighten the felt pen but cannot touch the biro - any suggestions short of re-painting

Apparently milk works on clothes with biro on them, so maybe on paint?. Also, I bought a sort of paste called "astonish" (or something similar), which got biro and pen off a coffee table. I think it's one of those "jmb" products that you always see in DIY stores - yellow and blue packaging - am waffling now so I will stop!

My ds has done this on his door and radiator, I found that jif got it off both very easily.

will try them both thanks