We have just released a set of patches for the issues that you raised.
The next URL is now correct in your brand/category/subcategary pages and we also return a 404 on listing pages without items.
With regards to the content duplication occurring when the URL normalization is enabled, Google was indexing both pages because the contents of their URLs were similar. The way around it is to send a 301 to the correct version of the page. For instance, for www.broughtons.com/store/search/brand/kirkpatrick-ironmongery/ and www.broughtons.com/store/search/brand/Kirkpatrick-Ironmongery/ since the former is the correct version, opening the latter URL would yield a 301 to the former.
In fact, this mechanism is already in place for retailers not using legacy URLs. Mind you, it may take some time before search engines reindex your store and at that point, I do expect to see a sharp reduction in the number of crawl errors.
Once again, I would like to seize this opportunity to thank you for reporting this issue to us.
Hope this helps.