Thank you for the long and detailed answer, theres some great advice there.
Basically both URL's have the right keywords in, it's just the URL was changed a while back so both still remain on the site. The newer URL is the one that ranks high on Google, the old one doesn't appear at all. There is no need for the old one, it serves no purpose that the new one doesn't. So surely getting rid of the old one won't affect the new ones ranking?
I see you put I should have full rankings back within 3-6 weeks, but there would be no reason why the URL that currently ranks high would lose any ranking surely?
Thanks again.