It looks to me (and all I did was a cursory 5 minute search so take my thoughts with a grain of salt) that your site is generating Page Titles dynamically.
So for example the pages in this category http://www.daytripfinder.co.uk/theme-parks/east-midlands returns the same page title for each sub category page but with the location changed dynamically, e.g.:
Category Page = Looking for a theme park in East Midlands? DayTripFinder
Sub Category Page = Looking for a theme park in Derby? DayTripFinder
BUT
If for any reason a user gets an error navigating any of these pages then you get served a standard error page that reads this:
Unfortunately there is no listing at this web address. Trying using the search form above by name or searching by location/postcode.
And when that standard error page is served the URL stays the same but the Page Title defaults to the Page Title of the error page, not the page title of the category page. All of the examples you list above served me the above error message.
So you're getting a duplicate content error messages because both the error message version and the regular version have the same URL.
Although, when I do a site operator with intitle I don't find tons of indexed category pages with the weird page title you list above, even though that's what I'm getting in the examples you cited. Which is weird.
But my guess is that it has something to do with how you serve your error message, although I would consult someone with more technical expertise to verify.