Oh wow, I absolutely LOVE this. The Speccy doesn't have a really decent Frogger and this is pretty much already the #1. Using character-square graphics to get the screen dimenions right is a genius idea and it really looks and feels like the arcade.
I very much hope you can track down the bug as it's annoying having to remember where you've landed frogs, but this is just a great piece of work beautifully presented.
(Only thing I don't like is four lives. What arcade game ever started with four lives?)