For anyone who has sat ATPL(H) exams in the past, and holds a CPL looking to upgrade in the future to ATPL this may be of some clarification. It's a few questions to the CAA on the issue with their responses.
In reference to your email regarding the validity periods for ATPL(H) and IR(H) theoretical knowledge examinations, firstly and in clarification JAR-FCL 2 ceased in the UK on 17th September 2012 and has been superseded by the EASA Aircrew Regulation (EU Reg 1178/2011) which is now law. The requirements of JAR remain mostly unchanged but there are some minor differences.
I have set out the responses to your queries but am using the current Part-FCL requirements which are applicable;
FCL.025 Theoretical knowledge examinations for the issue of licences
(c) Validity period
(1) The successful completion of the theoretical knowledge examinations will be valid:
(i) for the issue of a light aircraft pilot licence, a private pilot licence, a sailplane pilot licence or a balloon pilot licence, for a period of 24 months;
(ii) for the issue of a commercial pilot licence or instrument rating (IR), for a period of 36 months;
(iii) the periods in (i) and (ii) shall be counted from the day when the pilot successfully completes the theoretical knowledge examination, in accordance with (b)(2).
(2) The completion of the airline transport pilot licence (ATPL) theoretical knowledge examinations will remain valid for the issue of an ATPL for a period of 7 years from the last validity date of:
(i) an IR entered in the licence; or
(ii) in the case of helicopters, a helicopter’s type rating entered in that licence.
1. I completed the full ATPL(H) exams in 2005 - and subsequently was granted my CPL(H) in 2007.
I interpret FCL as saying, that my ATPL(H) theory is now valid indefinitely towards the grant of ATPL(H) because I was granted a CPL within the 36 months, and have since continued to maintain my CPL and a valid type rating.
Correct but only for the ATPL(H), this is not applicable to the IR which must be maintained within its own validities.
Am I still assured that under JAR-FCL 2.495 (b) my ATPL(H) exams will remain valid indefinitely towards the grant of the ATPL(H) provided that I have a valid type rating entered in the CPL(H)"
As above, yes, however this is conditional on you having held a valid type rating within the 7 year period prior to application.
3. People have suggested that the exams only have a 7 year validity for the issue of ATPL(H) (not whats suggested if you comply with JAR-FCL 2.495 (b)) - am I reading this incorrectly or are they are referring to what is found in JAR-FCL 2.495 (c)
Yes, for ATPL(H), however the IR must be obtained within the 36 month period from passing the final ATPL(H) (under amendment 3 of JAR-FCL 2 or ATPL(H)IR exams under Part-FCL). As you have passed the IR exams in 2011, these remain valid for 36 month for the addition of an IR to your current CPL(H).
It must understood that for Helicopters, the ATPL and the IR are no longer conjoined as in the past. It is possible to hold an ATPL(H) VFR and add the IR at a later point if required.
JAR-FCL 2.495 (c) states - Provided that an IR(H) is obtained in accordance with (a) above, a pass in the ATPL(H)[/IR] theoretical knowledge examination will remain valid for a period of 7 years from the last validity date of the IR(H) entered in the CPL(H) for the issuance of an ATPL(H)
Correct.
There are a number of people in the same situation as me asking for clarification on this, and whether new EASA regulations have changed this or if the JAR FCL 2 still applies to us, given it was in effect when we sat our exams and were granted our licenses.
The text of FCL.025 (above) applies, although it is the same as the provisions of JAR-FCL.
The main question for me is - in my case does my ATPL credit still remain valid indefinitely, so following the completion of the IR I simply need to meet the other hourly/MCC requirements and assuming my CPL and IR remain valid there is no time-frame in which I must be presented for the ATPL test?
Yes. Although you may want to re-sit the ATPL exams again in the future purely for the pleasure and to refresh your knowledge?? He has a sense of humour 
if you could confirm whether all of the above is true then I will be able to pass on that information to my colleagues who are asking so we all have a better idea of what should apply.
Confirmed, with the clarifications as above.
I hope this information satisfactorily answers your query.