I stumbled upon "on the spur of the moment" in wiktionary.com  and
found that the meaning given is "on very short notice". The example
cited reinforces the meaning -"They kept their bags packed so they can
leave on the spur of the moment".
I thought the idiom referred to acting on impulse as in " I took that
decision on the spur of the moment and have regretted it ever since".

"Paul"  wrote in message 
news:7fb88046-2200-401a-8353-45277fb7b0bc@a32g2000prf.googlegroups.com...
> I stumbled upon "on the spur of the moment" in wiktionary.com  and
> found that the meaning given is "on very short notice". The 
> example
> cited reinforces the meaning -"They kept their bags packed so they 
> can
> leave on the spur of the moment".
> I thought the idiom referred to acting on impulse as in " I took 
> that
> decision on the spur of the moment and have regretted it ever 
> since".

My own view coincides with yours, but the OED (1989) allows for 
both:
d. /on (or upon) the spur of the moment (or occasion, etc.)/, 
without premeditation or deliberation; on a momentary impulse; 
impromptu, suddenly, instantly.
-- 
Noel