Freelance engine payment Software

Hi I am looking at getting a payment system working on my website which will currently work through paypal and from you bank cards with normal payments. It will be for a freelance engine theme. The whole plan is to have something set up similar to this website where you pay the project cost and then the freelancer does the work and the project owner is happy with the work done the funds will then be released. The website will be taking a % of the final fee for commission for using it through the website. So example....project is of value of £20 a freelancer bids for the project and wins. The £20 will be paid and held till the project owner is happy with the work that has been done and once happy they release the £20. A commission of what I have set will be paid to the website for using the service. Any questions please feel free to ask. Thanks