Fined for being partially in bus lane - worth appealing? What is the law on this?

Unfortunately, the law interprets it as any of the four wheels being in the bus lane means the offence is complete - think of solid white lines on the road (obviously rather more serious) - you don't have to take the whole car across the white line to be prosecuted. You can try an appeal but I doubt you'll be successful - don't forget punishment can be increased on appeal as well.