I'm doing the other half of the paper (Henry VIII), but exam technique is the same. I think the way to approach it is to explain what the MP is saying, and his conclusion. Then, in the same paragraph, write about how the provenance affects the reliability of the conclusion. At the end of the paragraph you can do a little concluding bit about how strong/weak the argument is. In 20 markers particularly I think it's acceptable to approach it as evaluating the arguments on each side, not actually writing a strong argument for each side, if that makes sense? I.e. Evaluate how good the arguments presented in sources are.
So yes, I'd put the provenance (even if negative) in the same paragraph as source analysis, always. Hope that made sense.