Complex sentence: The position is different in Scotland, where it is lawful to agree that the lawyer gets paid only if the case is won (the "speculative action") but not to fix a percentage of the client's winnings as the amount of the fee.
Split into simpler sentences: The position is different in Scotland, where it is lawful to agree that the lawyer gets paid only if the case is won (the "speculative action"). It is not lawful, however, to fix a percentage of the client's winnings as the amount of the fee.