Who decides what kind of devolution

English votes for English laws.  Has a certain ring to about it. 

I’m assuming all these MPs representing English constituencies will therefore not take part in a debate and vote on what form more devolution to Scotland should take.   

That surely will mean that only those representing Scottish constituencies in Westminster will be able to vote on which of the many and very different options of more devolution for Scotland is selected.

Or will it be imposed by the English MPs?