Many thanks for both your replies. It looks like, as far as the 1960s are concerned, the Mitchell Mer and Mitchell 302 are the same reel. With regard to the photo of the box, it would appear that the term 'Mer' was subsequently applied to later models as well.

I have seen a reel called a Mitchell Mer listed for sale in advertisements in a UK magazine called Fishing, published in the 1960s.
Is this the same reel as the Mitchell 302, or a different reel?
I need hard facts; not speculation, as I am publishing the information in a book.
Many thanks.