Misprint - 1 pound British bank note

I have a 1 pound note from the Bank of England that was either printed or
came into our family's possession in 1978, but with a printing error. It is
supposedly one of a kind and the misprint involves a black line in the note
that is too close to the face of the Queen (clearly visible when the note is
held up to a light, but still visible otherwise). The serial number is A70
972667 as it appears on the lower right side of the front. The signtaure of
the Chief Cashier appears to be one J.O. Page and the rear bears the
likeness of Sir Isaac Newton. The note is in extremely good condition and,
if circulated, it hasn't been touched by many hands. It has no folds or
creases, or other markings. As soon as I can, I will try to get a picture of
it that may be available online. I am curious as to the possible value and
interest anyone might have in this bank note.