Forgive me for my naivety, but if Rory Stewart is your local tory candidate, how could voting for him be a vote for Thick Lizzy?
Because in our current system if you vote for a local Tory candidate you are, by proxy, voting for whoever the Tory party leader is to be PM.
And while in an ideal world everyone would go to a GE and choose the best local candidate to vote for, in the real world the majority vote for whoever represents the party that they want in government (and by extension who they prefer to be PM).
In some seats that's not the case and you do get enough people voting for the local candidate specifically to swing a result. But there's other seats in this country where you could stick a blue rosette on a pig and it'd win.