Before you begin your conversion...
...make sure you know what's involved.
If you are converting a non-JAA ATPL the number of ground and flight tests you need to complete depends on your experience.
High Time Pilots
If you are very experienced you should you should apply to the CAA for a formal assessment using Form SRG 1103. Read Lasors on more about this.
The qualifying criteria are
more than 3000 hours total time on aircraft of more than 30,000kg AUW
more than 1500 hours pilot in command on aircraft of more than 30,000kg AUW
type rated on an aircraft of more than 30,000kg AUW
more than 500 hours total time on the aircraft above
able to complete a flight test on the same aircraft
When you have completed the assessment form you need to send it or take it to the CAA with your original licences and log books. The CAA will tell you that you need to pass two written exams, Human Performance and Aviation Law, and pass a flight test on the aircraft you are rated on. The flight test is referred to as a skills test, it is part handling check and part IR renewal check.
Experienced In Two Pilot Operations
If you don't meet the criteria above but have
more than 1500 hours on two-pilot aircraft,
are type rated already and
have more than 500 hours on type
you need to pass all 14 ground exams but don't need to attend a formal groundschool course. You will need to pass a skills test on the aircraft you are rated on.