Generate a page per council (eg: /council/<slug>) which includes all the same content as the homepage, but with that council’s name and details in the meta tags (including social sharing image URLs #8)
Make sure council pages have a canonical tag pointing back to the homepage, to prevent them being treated as duplicates
Use the JavaScript History API to update the browser URL (without navigating) when a council is "selected" through postcode (#5) or name (#6) search
…and to reset the URL back to normal when a council is "deselected"?
Nice to have: Visiting a council page should pre-select that council in the list / on the map
/council/<slug>) which includes all the same content as the homepage, but with that council’s name and details in the meta tags (including social sharing image URLs #8)