According to received history, Roosevelt conceived Land-Lease on
December 16, 1940 (shortly after he had been re-elected for a 3rd
Term.)

There is now compelling evidence that this was actually being debated
between the US and Britain in May 1940.

Am I the first person to have uncovered this proof?

Or has it already been reported?

(I know there was some speculation at the time and also some
uncorroborated claims since but, as far as I know, this has not
hitherto been PROVED.)

Dear Bryan,

Thank you for allowing me to post this as an answer. Sorry I could not
achieve anything better. Perhaps the answer still lies hidden deep in
the bowels of the PRO at Kew.

This is the only reference I could find - 

"On June 10, 1939, George VI and his wife, Queen Mary, visited the
Roosevelts at Hyde Park. In private conversations with the King,
Roosevelt promised full support for Britain in case of war. He
intended to set up a zone in the Atlantic to be patrolled by the U.S.
Navy, and, according to the King's notes, the President stated that
"if he saw a U boat he would sink her at once & wait for the
consequences." The biographer of George VI, Wheeler-Bennett,
considered that these conversations "contained the germ of the future
Bases-for-Destroyers deal, and also of the Lend-Lease Agreement
itself." In communicating with the First Lord of the Admiralty,
Roosevelt was aware that he was in touch with the one member of
Chamberlain's cabinet whose belligerence matched his own."
http://www.lewrockwell.com/orig/raico-churchill3.html

The book referred to above is detailed here -
http://www.biblio.com/books/4716107.html

Season's greetings
answerfinder-ga

Hi, Again AF

Many thanks for your Answer.

I'm planning to go to Kew on Sat Jan 3 and I intend looking if there's
anything there.

In the meantime, have a Fantastic Festive

Bryan

Hi, Bryan

The following doesn't actually refer to the events in May 1940, but
may interest you:

http://history.acusd.edu/gen/st/~mdoms/toc.html

Merry Christmas and a Happy New Year,
Freddy

Hi, Freddy

Many thanks for your Comment.

Much appreciated, as always.

Have a GREAT Festive Time, yourself.

All the Best

Bryan

This is the only reference I could find - 

"On June 10, 1939, George VI and his wife, Queen Mary, visited the
Roosevelts at Hyde Park. In private conversations with the King,
Roosevelt promised full support for Britain in case of war. He
intended to set up a zone in the Atlantic to be patrolled by the U.S.
Navy, and, according to the King's notes, the President stated that
"if he saw a U boat he would sink her at once & wait for the
consequences." The biographer of George VI, Wheeler-Bennett,
considered that these conversations "contained the germ of the future
Bases-for-Destroyers deal, and also of the Lend-Lease Agreement
itself." In communicating with the First Lord of the Admiralty,
Roosevelt was aware that he was in touch with the one member of
Chamberlain's cabinet whose belligerence matched his own."
http://www.lewrockwell.com/orig/raico-churchill3.html

The book referred to above is detailed here -
http://www.biblio.com/books/4716107.html

answerfinder-ga

Hi, Answer Finder

A good link. Many thanks.

It's not the answer I was looking for but I will accept it for want of
anything better ...

So QUICK, post it as a Comment.

Have a Great Festive.

Bryan