As BigBird said, the CAP509 course is the ab-initio Frozen ATPL course (so called because the book defining the requirements is CAP509).
Given sufficient aptitude and motivation, a student can go from no prior knowledge of aviation to a CPL/IR and frozen ATPL in less than 60 weeks, in theory at least ready to go to an airline. A good LOFT (Line Orientated Flying Training) course at the end would make the 509 grad much more employable- in fact, most airlines who sponsor students provide LOFT courses.
To be approved for 509 courses, a school must satisfy the CAA about:
Experience level of instructors (MINIMUM of 1000 hours P1, 500 Instructional). All instructors to be tested by the CAA specifically for the course.
Standardisation (ie, if a change of instructor is necessary, no relearning of fundamentals required)
Course syllabus
Equipment
Groundschool facilities and instructors also to be individually approved.
A 509 course typically involves around 180 flying hours, plus simulator time. Of this, 100 hours is P1, the rest dual. To ensure the solo time is spent effectively, there are also limits set on solo time between dual flights- this should minimize the chances of bad habits being acquired during an hours-building phase.
Tests roughly equivalent to PPL-GFT, IMC Test and Commercial GFT are set throughout the course, and carried out by in-school staff. The final Commercial IR Test is done by the CAA.
Prices vary widely between schools, starting at about GBP30000 (I think).
If going for a JAA licence, the course has fewer flying hours, the same groundschool. The jury is still out as to whether CPL standards can be reached in these fewer hours, or whether there will be extra hours required at the expense of the student.
Before spending the money on a 509 course, get yourself aptitude-tested (arrangements have been made for civilians to be tested at the RAF's testing centre at Cranwell, through the Guild of Air Pilots and Air Navigators- check your back issues of Pilot for contact details). If you score badly, DON'T COMMIT YOURSELF TO SPENDING A FORTUNE WITH NO GUARANTEE OF SUCCESS. It's not an automatic disbar from a CPL- just get a PPL and try the tests a year later. The CAA usually give a small reduction in the required time (and therefore cost) of your 509 course if you have a PPL.
As of January 1999, FlightSafety International is not accepting new students for 509 courses, but there are still places at the UK schools if you negotiate starting dates carefully.
Good luck, email me if I can help you.