I don't think that poor first year grades in this situation will prevent you from getting onto a Bar course. Some have a 2:1 minimum, but the BSB minimum is 2:2 and some providers still go with that. You will need someone who has more recent experience of the application system to tell you how they go about assessing your academics when making offers, or you can email the providers themselves is there are one or two that you'd be aiming for particularly, but places on the courses themselves are not oversubscribed and there should not be an issue getting on one, even if it's at one of the providers that has a 2:2 minimum. I expect as long as you come out with a 2:1 at the end it won't matter, but as I say, you'd need to check with someone who has more direct knowledge or with the providers themselves to get that answer.
Either way, this issue won't prevent you from being accepted by an Inn, and providing you come out of your degree with a 2:1 and then do the Bar course, your first year grades will be practically irrelevant for the purposes of pupillage applications. As has been said already, where you do the Bar course doesn't matter. So in the grand scheme of things, this issue isn't one that should impact your chances of getting pupillage ultimately.