Appointment Management Software to replace Appointment Plus

I run a small private medical practice in the UK and we have been using the Appointment Plus software for several years to manage our booking system, room allocation, and client appointments. Over the last few months, however, they have decided to "upgrade" their software with the result that it has become nearly unusable. The system has a front-end, which we link to from our website so that clients can book appointments online in available slots. It has a back-end where we have configured our treatment rooms, timetable and can colour-code appointments as attendees and no-shows. It acts as a client database and various reports are available, including exporting all contact details for clients, and listing all upcoming appointments in a csv file. We do not use the functionality for online credit card billing, but appointment reminders by email would be necessary. We are looking to obtain a system offering very similar functionality that we can run on our own servers, which are already hosting our website. As far as I am aware the existing system is based around a PHP database with an HTML interface. The job specification would require a functioning model, which we could test before we migrate across with our exisitng client data and appointments list. All client data would have to be held securely and in complete medical confidence. Our timescale is flexible, but I understand that the "classic" interface on Appt Plus will only be continued until the end of October 2011 so to get a clear idea of our current system and functionality that we will be looking for, we only have until the end of this month. Please feel free to post any requests for further clarification and I will answer them as well as my technical knowledge permits. Thank you.