Well, yes, it is against policy because the 3rd aspect (after 12 subs and built in SA) was Non Nuclear.
Either way, it is all political based decision making as was shown in one article as one major aspect they are looking at is interoperability with the US who they know they will be working closely with - most of us would say just use what they are using (assuming they will sell them current class to allies - not sure on that one).