baldwinm -
1. Look in the front of your old PPL and check whether it states (probably in para IX): ' This licence shall remain in force from (date) for the holder's lifetime unless revoked, suspended or varied '. If so, then it's a UK lifetime PPL. But you can't enjoy the privileges unless you have a valid 'Rating' - and that's what you'll be 'renewing'.
2. To renew your Single Engine Piston (Land) Class Rating, as you haven't flown for over 10 years you'll be required to do the following - obviously you'll need sufficient training to do so:
2.1 Hold at least a JAR Class 2 medical certificate.
2.2 Pass the SEP renewal proficiency check with an Examiner.
2.3 Pass an oral examination conducted by an Examiner as part of the check.
2.4 Send all the paperwork off to the CAA with the relevant fee. State quite categorically that your hold a lifetime UK PPL (if you do) and do NOT want a JAR-FCL licence (which are only valid for 5 years).
3. I agree that the FRTOL question is unclear. It does indeed state quite categorically that where a UK national licence has been issued with lifetime validity, the FRTOL will be deemed to be valid as long as the associated flight crew licence remains valid. But if you haven't 'exercised the privileges' of your lifetime FRTOL for more than 10 years, then it seems that you'll need to do the whole RTF test (theoretical and practical) again.
But what constitutes 'exercising the privileges' of the licence? For example, if you have been flying with another PPL holder and have used the radio, would that count? I don't know - you'll have to press the CAA on this as the guidance in LASORS isn't sufficiently clear on this.