Is there any way that Munchkin, or some form of cookie tracking can storm the original UTM in a cookie from a Marketo landing page...
To echo @Edward, no purely
cookie-based tracking can pass values from pages.landingdomain.co.uk to www.jpr.com, because they do not share what I call the eSLD (effective second-level domain -- basically, the types of domains the public can register). By contrast, pages.landingdomain.co.uk and www.landingdomain.co.uk share the eSLD
landingdomain.co.uk, and www.jpr.com and jpr.com share the eSLD
jpr.com. If your sites share an eSLD, you can link cookies to the topmost eSLD, so they'll be shared across both sites (Munchkin does this by default).
But if your Drupal pages and Marketo pages don't share an eSLD you have to find another way to pass tracking cookies around. Since the Munchkin cookie is nice and small, you can actually pass it in the query string. To do this, use JS to append the current Munchkin cookie value to all your hrefs (or all offsite links). Then have the other site set a cookie with that value (if it doesn't already have one)
before loading Munchkin. You have to do some smart JS coding to make sure you use the "most known" Munchkin value, for example if a user is associated on Site 1 but anonymous on Site 2 you want to get the Site 1 cookie onto Site 2 but not vice versa.