PHP / MySQL back-end developer

We are looking of PHP developer with MySQL experience to expand and maintain the back-end of a mobile messaging system. This messaging system uses Apple's Push Notications and Android's Cloud to Device Messaging. The expansions consists of e.g. statistics (including some data mining because of the large amount of data), a basic role-based security system and other optimizations.

The back-end UI is made with Code Igniter(http://codeigniter.com/), experience with CI is bonus.

Preferably we are looking for people located in Europe (UK, Western Europe).