Ex-Yahoo! , CEO of Yellow Square and startup consultant.
You need somebody with excellent PHP knowledge to give you peace of mind that your code is secure and robust.
I'm a UK based developer and have over 14 years' professional PHP experience so am in a good position to perform this for for you. I have worked for some of the largest and most respected companies on the web, including Yahoo!
As well as verifying your source code, I will can comment on your general architecture and your system configuration. For example, many PHP security issues are not directly related to the code, but rather how it is configured on your server.
(photo credit: David Goehring)