Junius and Sir G. Jackson

I find no one has answered my question about Sir George Jackson (No. 11. p. 172.). I will therefore put another. I possess an unpublished letter by Junius to Woodfall, which once belonged to Sir George Jackson. My Query is, "Is it likely he could have obtained it from Junius, if he was neither Junius himself nor a party concerned?" The manner in which Burke evades the question as to himself being the author of *Junius* makes me think two or three were concerned in these Letters.