Essential background: I run a small company that lets members of the public post handwritten letters to their local politician (UK-based). Every week a number of early stage bills (called Early Day Motions) are submitted for debate in the House of Commons, and supporters of the motion will contact their local Members of Parliament, asking them to sign the motion.
The crux: I want to target these EDMs with customised mini-sites, so when people search "EDM xxx", they find my customised mini-site, specifically targeting that EDM (i.e., "Send a handwritten letter to your MP asking them to sign EDM xxx").
At the moment, all these mini-sites (and my homepage) have duplicate content with only the relevant EDM name, number, and background image changed.
The question: Firstly, will this hurt my potential search engine ranking? And, if so, what's the best way to target these political campaigns in an efficient manner without hurting my SEO prospects?