Yippee… the site is up and running… here’s the info …
https://contacts-demarches.interieur.gouv.fr/brexit/brexit-demande-titre-sejour/
In English…
https://contacts-demarches.interieur.gouv.fr/brexit/brexit-residence-permit-application/
and here’s the flowchart in English
Thank you Stella, all seems straightforward, I’ll make an attempt later today. 
@Stella Thanks Stella, really easy.
All done and dusted, not difficult although having asked for surname in capitals and given names only with a capital first letter, it then demanded all capitals. 
I noted also that I have now been knighted, my correct form of address is Sir David Marker. I hope you will all remember that when addressing me in future. 
But the biggest surprise, it only asked for a copy of my long expired CdS, but not my passport. What was required were details of my passport including number, so perhaps they have a direct line to HMPO.
Will go though the same procedure for my wife later.
Now if only sorting out our bank accounts and our cartes vitales were as easy!
Do it quickly as if you need appointments (you may not if you already have been finger printed) and you put them in one after another you’ll get appointments at a similar time. If you leave it she may end up next day appointment which may be a pain depending how far you live from the prefecture.
The suggestion is for everyone to have both ready to go and do one after another for this reason.
We have been waiting for our translated BC’s…and we don’t need them, gawd! 
Thanks Tory, done it now 90 minutes after mine and around 4,000 between us. Never thought about rdv dates maybe being consecutive, it would be inconvenient on different dates at 100 kms a time but it will be the only time in our lifetimes that we need them I reckon.
One thing I never noticed before. We renewed our passports at the same time on the same date but while mine expires in November 2025, hers not until February 2026. 
Err…if I am Sir David now, shouldn’t she be Lady Frances instead of plain old Madame? 
probs the expiry dates on the two old passports were different… 
Ours now done as well (also Knighted courtesy of the RF) basically quarter of an hour each with no break between and the number of applications jumped 524 - impressive on-line facility 
My missus is now a proper madam 
Having read through the information provided on SF (courtesy of @Stella and @toryroo - many thanks for which) the process was extremely straightforward an in no way onerous or challenging.
I’m so glad to get this positive feedback… after all the worry many of us have been going through… nice to feel something is working well… 
Help please. I am stuck on the Channel Number, Extension, Label of the Channel. What is meant to go in there? TIA
Channel Number is your house number…
Ah, thanks very much.
Just one curious thing…
On my application (which we did first) I was asked at the end to respond to a security question (subtract one number from another) but on V’s application immediately following it there was none 
Fortunately, being somewhat numerate, it wasn’t difficult but it did make me wonder at the time if applications are only accepted from enumerate Brits 
@Susie_Kelly Ah… just looked back on our app… Building-Residence = number of name but Channel number = (in our case) LDT (lieu-dit and it’s name) but if you look on the back of your existing CdS (if you have one) type in the address as shown…
Thanks for that, Graham - that section had me scratching my head and doing a quick bit of Googling!
Google is your friend - sometimes but probably not in this case
and sorry - just to emphasise a point, this question was already addressed in another thread here by @SuePJ - too many threads on the same subject can cause confusion and missed pointers 
Bonjour
Was awake early this beautiful morning, made a cuppa, and headed to the computer, started completing the brexit application on line, took note of the GED code, wrote it down, then was interrupted, on my return the page had timedout,.
Found the gouv.fr page for applying for new carte de sejours, took note of the new GED code completed the page pushed the Suivant button’ this is where it all goes wrong, the GED code is not accepted, it was typed exactly , husband checked it, yes that is the same.
Have been all over the site to find how I can move forward, even went to the laptop and started afresh, with a new GED code, and still same reject.
Have now knotched up about 10 of these GED codes.
Has anyone else been down this avenue .?
Any helpful suggestions
@toryroo may have some indications on that issue…
On my application I entered the reply to the security question in text. Then validated the application. Nothing happened. So I went back and entered a numeric response, and when I validated had a message that the application had already been submitted. But didn’t get any notification by email.
When |I did my husband’s application and validated, I received a green form saying the application was received and there was a green notice with an application number and promise of an email to follow. I didn’t get that with my application.