This is the reply I received from the CAA on 11 July this year:
The proposed amendment to the ANO is imminently to go to the Department for Transport for transposition into the law. This process will take some 3 months. The amendment changes the reference to JAR-FCL to Amendment 5 (although we will have Amendment 6 before that happens!). Until then Amendment 3 is the reference which permits (or can be interpreted to permit) the use of FNPTs for IR revalidation and renewal. There is still a question mark over whether this change will need to go to open consultation as it may have a cost impact in having to use an aeroplane for renewals and alternating revalidations. However, the number of pilots affected should be very small as IR revalidation is normally combined with the class or type rating proficiency check. It would thus normally only apply to the holder of a multi-engine IR who is only flying SEP class aeroplanes. DfT will no doubt decide. Once the proposed amendment is laid before parliament we will know the effective date of the legislative change.
a) I disagree with his comment that 'the number of pilots affected should be small' (and told him so - with no response of course). In our experience most of our IR renewals are only renewing the IR, not the MEP, as they want to have a current IR on their cv, but know that the airlines are not interested in the MEP being current.
b) the new rules are likely to be implemented sometime around October this year. Until then the old rules still apply, i.e. you can do a renewal, or a revalidation, in the FNPT2 every year.
It is a revalidation if you do it before the expiry date, and a renewal if you do it after the expiry date.
One point to note is the fact that once this rule is implemented you will not be able to use the FNPT2 to renew your IR, i.e. once you pass your expiry date (even by one day) you will have to do the renewal in the aircraft.
Linda