I think it is more likely that Andy has an original birth certificate, which is proof of identity, rather than a recent GRO replacement. (but none of our business)
A call to the Library and the duty Librarian confirmed that an English birth certificate is fine as the directive (for Andy's case) says birth certificate without any qualification or restriction.
However I have also added a written query under our ref-tracker question so you should receive written confirmation and/or clarification Andy. I'm just leaving it up to you to follow through with this overall query about your father's time in Australia Andy (but I'm happy to help if you need me
).
The library staff are extremely helpful. You've probably seen that they also suggested several books which you may find interesting.
Ros
