Fixing 404 after permalink change

I have changed my permalinks on my site and installed a 301 redirect plugin to fix links that would be broken, but it isn’t working.

Old structure: /%postnmae%/
New structure: /%category%/%postname%/

e.g. this link

http://roundreviews.co.uk/quicksilver-canvas-folio-iphone-5-5s-case/

doesn’t redirect to

http://roundreviews.co.uk/reviews/phone-cases/quicksilver-canvas-folio-iphone-5-5s-case/

Is there anyway I can do this?