Whats the difference between a ATPL and a CPL/IR ?

Say about 2 years worth of flying (to reach the required 1'500 hours), a sim check (normally integrated into the LPC, as it gives the TRI more time for jokes), and some paperwork

Thanks for that F4f

Not forgetting another cheque to the Ministry...

and a load of ground school and 14 exams e.g. http://www.bristol.gs/

And also the slight problem about not being able to get into the left seat of any decent-sized aeroplane without an ATPL.

...and you lose your nice blue licence cover and trade it for a yukky looking green one....
Still it isn't as yukky as the brown one

The principle difference is that CPL/IR does not require specific multi-crew training where the F/ATPL does in the form of an approved MCC course in an approved multi-crew simulator.