There is a thread HERE with information on how to fill out the Certificado de Registro application form, and the procedure to follow to get your Certificate.
After getting all the correct documents (except the medelo) as per @Duderock's sticky post, I joined the queue at 7:30am this morning. There were about 30 people ahead of us.
At 9:15 two policia came out, and separated spanish nationals from extranjeros (no idea why) into 2 queues.
As we got to the front, they asked us if we had 'paid the tax' which we hadn't, so no ticket. We went in and got the modelo 790s and off to the bank.
Back at the police station at 10am, and got a ticket A29, when they were seeing A23 at the time.
Half an hour later, we were the proud possessors of the 'magic blue-tinged certificados'
We were lucky. The lesson from this is to make it a 2-stage process: call in during the day to get the modelo 790 and process it at your bank. The
next morning - join the early queue.
Thanks to @Duderock - without his info, we could never hae done it
