I brought this issue to some friends of mine who are GP´s and actually they also have to do many referral letters to consultants or hospitals. They are allocated some time to do admin and referrals after seeing their patients. They were surprised the way we Optometrists have to work.
In my own experience, I prefer to do referrals immediately after examing the patient and hand it to him/her. It may delay the clinic a little bit but it works better.
When I started locuming years ago, I remember leaving all the referrals to the end of the day. I remember saying to the staff to bring the records back to me once they dispensed or updated them in the system. BIG MISTAKE, because in several practices they used to forget to do it and I had to chase them until I got them back.
Other problems with referral being posted is finding doctors addresses and post codes. In some practices is very difficult to find the doctors directory and if you are lucky to get one quite often are not updated and many doctors do not appear. Being honest in most practices will help you with this issue and find the doctor´s address for you but in some others they refuse to do it and it delays the whole process of writing the referral. If you only have to do one referral you will handle it, but the problem arises when you have to do several of them.
Conclusion: do the referrals after seeing the patient and hand it to him/her unless you have reasonable suspicions that the patient is not going to take the letter to his/her GP.