If you look at the very first posting on this thread, it mentions that the Conservative Party had lost two by-elections in a row. Howsoever, at the last General Election, they had a much-increased majority from the previous General Election, so the loss of a couple of by-elections would not make as much damage as would have been the case in the previous administration.
Oh, not so sure about that. A squeaky-bum tight result in the south west and there'll be a good few Conservative MPs looking nervous, and a loss (which I find extremely unlikely) would be game on for a leadership challenge IMHO. The balance in the Commons might not change, but a collapsed majority in a true blue seat would send a message that's pretty hard to ignore for a lot MPs.
FWIW I consider myself to be mildly to the right of centre overall, somewhat more likely to vote blue than red, but also one who floats and is a long way from a guaranteed vote for any particular party. I voted Labour at the recent locals purely because I'm absolutely sick of Boris acting like a naughty teenager - lie first, then try and get away with a sorry when cornered. I simply don't trust the bloke in the sense that I don't trust politicians generally but he's on another level. I wouldn't lend him the lawn mower.
That said, IMHO, as to where it'll genuinely go wrong for the Conservatives is if Labour can find their Adult Trousers and put together a coherent set of policies that positively targets sections of society other the usual suspects - the desperately poor, dogmatists, those still in puberty, and pressure groups. That's what did it in '97 to great effect. If they can't then the "Most Egregious Miss of an Open Goal in British Politics" award, currently held by Neil Kinnock and Co. is going to be looking for a new home on Sir Keir's mantlepiece. Niffy incumbents don't just keel over because they niff, they need to be pushed out by something that's demonstrably more palatable to a good few million neither-rich-nor-poor J. Random Brits.