Renamed blog permalinks and have loads of 404s

I foolishly renamed a load of the permalinks of many blog posts on my site and also re-did my tags too as I had a load of tags with single posts and removed them. Google webmaster tools is now picking up loads of missing pages and duplicate meta titles and descriptions, even though the page is no longer there. Any ideas?

Ive just installed the 404 Redirection plugin to redirect missing pages to home page, but not sure to do with the duplicate meta as I only have one page per blog but google is picking up several pages per blog.

Thanks