When would a basic "finder's fee" agreement be unenforceable under the laws of England and Wales?

I'm a co-owner of a US based LLC, established to help a UK company grow its business and potentially find a US-based acquirer. My business is strictly acting in the capacity of a "finder", compensated via a variable success fee if our introductions turn into sales. The UK business owner is requiring the contract be governed under the rules of England and Wales. Are there implications or risks that we need to understand vs US law? And more importantly, are there any reasons to be concerned the agreement would not be enforceable if we accepted the rules of England and Wales?