RE "Scottish ingenuity is--like British humor--not to be laughed at"
and "If you had brains"

"not to laughed at" means the same as "to be taken seriously"
Aha. The original statement is the same as:
"British humor is to be taken seriously, because it is funny"

or, in other words:
British humor is not to be laughed at, because it is funny.

.....or, if you had brains you would....