Does anyone know the origin of the phrase "all my eye and Betty Martin"?

Answer 1

Have a look at this - it is a previous answer and gives a latin phrase "mihi beata mater" as the origin.

http://uk.answers.yahoo.com/question/index;_ylt=AoYCFAftVa7gX2Mhirmi8qVJBgx.?qid=20070518115703AAxyEmk

Answer 2

There seems to be a possiblity here:

http://www.fromoldbooks.org/Grose-VulgarTongue/b/betty-martin.html

And a discussion here:
http://www.worldwidewords.org/qa/qa-all3.htm

Of course, as we go further back in history, things get a bit murky, and other explanations arise.