What's the name of the BBC program that showed squirrels being put to
the test against an elaborate obstacle course?

I am certain that you're thinking of the delightful BBC programs
"Daylight Robbery" and "Daylight Robbery 2," which depicted some
remarkable acrobatics performed by squirrels as they proceeded through
obstacle courses in pursuit of edible goodies.

You can view some clips here:

Squirrels.org: Video Clips
http://www.squirrels.org/t_video.html

Google Web Search: "bbc" + "squirrels" + "daylight robbery"
://www.google.com/search?hl=en&ie=UTF-8&q=bbc+squirrels+%22daylight+robbery

I hope this helps! If I have not correcly identified the program, or
if anything is unclear, please request clarification; I'll be glad to
offer further assistance before you rate my answer.

Best regards,
pinkfreud

Fantastic! Very complete. Exactly what I was looking for.

Please excuse a typographical error in my answer. 

For "correcly," please read "correctly."

Sometimes the fingers type more rapidly than the brain can think.

~pinkfreud