Splosh,
In answer to your question, I don't think this is written down. It's a bit like a secret map to navigate around a mine field.
As I understand it, it's an 'implied' solution, which also worries me with the current wobbly goal posts. What they have said is that you can convert a current CPL IR to a JAR CPL/IR (R). If you have more than 500 P1 (I think), they will remove the restriction (R). The ATPL written passes are also credited to you, and remain valid for 7 years from your last IR renewal. This is in the JAR stuff.
Hope it helps. My advice if you are worried about it is to write to them directly, asking for answers to your specific questions, and also asking them not to send you the answers with a compliment slip attached to AIC's. Give me an email address and I can give you a name of someone to send your stuff to in person. Works for me.
PS - usual caveates apply.