I also froze the cake in advance as suggested (first time i have done this to), but it really helped with moulding the cake, and did not impair on the taste of the cake at all! Thomas's face, wheels and lights were made from fondant. the rest was frosting, including the coal in the back of Thomas which I piped individually.
The cake was a big success, and made my little boy very happy! The entire cake was eaten!
I also made cupcakes in yellow cake and iced them in blue royal icing. the toppingscame from a cake box mix that I bought whilst in England containing edible rice paper images of Thomas and Friends and royal icing mini train sprinkles! Perfect!