Jar, Ano, Easa
Being of an engineering background, not legal, I hope this helps.
In 1979 an arrangements document was signed in Paris by ten states, which later increased to 27 States. This document committed the Participating Authorities to maintain JAR, and set out the ground rules for acceptance by signatory states of products complying with JAR, and established the Joint Aviation Authorities.
The above is taken from CAP562. The JAR were regarded as an Acceptable Means of Compliance and / or Guidance Material. Many JAR were never enshrined in British law, the most notable being JAR-OPS. Government lawyers decided not to include it as there was a general understanding at the time, that the Europeans would do the job for them by including it in European law. This has taken much longer than originally envisaged, although JAR-OPS sub-part M (maintenance management) has been superseded by EASA part M. JAR145 (maintenance) was one example of a JAR that was included in British law.
The EASAintention is to include EU-OPS (JAR-OPS) and EU-FCL (JAR-FCL) in European law by end of ‘08.
As the JAR are superseded by EASA, most of the JAR requirements now just cross refer to the relevant EASA legislation – see JAA website.
Ref. your point concerning the ANO. Sect 1, part 4 pg5, para 4(b) refers to flight crew licences:
(b) a JAA licence shall, unless the CAA gives a direction to the contrary, be deemed to be a licence rendered valid under this Order.
Hope this helps.