Intractable problem?

Perhaps I'm being thick but I can't see why the idea of "English votes for English laws" would be that difficult to manage in practice - at least the English votes part. We know which MPs represent which constituencies so where's the problem?  I see a far bigger issue being in identifying "English laws".  Suppose for example that Scotland decides to set its corporation tax at 25%, and then the Westminster government proposes to set England and Wales' corporation tax at 23%.  You could argue that this is a decision for England and Wales only, but clearly it will impinge on Scotland - which is still part of the UK, so can they be denied the right to have their say on it?  Of course the problem is that if you turn it round - Scotland proposes to introduce a lower rate of corporation tax than us - we would and could have no say in that decision. This is the West Lothian Question in all its glory, and I have no answer to it, save to say that we should never have agreed to Scotland having a devolved parliament in the first place.  The problem is and always was inherent in that decision.