Got about as far as you, Graham, but the App kept going slow, so the promised Code never appeared. So I pressed 'Send' again, and still no Code; then I tried an individual Form, instead of a Family Version and pressed 'Send' again; no Code. So I pressed Send again, and, about 1/2 later I received 4 Codes! Rang Brittany Ferries ['BF'] re timing of Form and UK Gov advice that a paper copy could be submitted; Glen at BF said 'You're not the first person I've had this conversation with; we'll try to help you with the form at the Port, but we're not geared up, and the Form is designed for those on a 4 hour flight, not a 2 day sailing ...'
In view of the requirement to make a £600 booking, including cabin, so that I could get a QR Code on the day of sailing, with a system as clunky as this, we decided to abandon sailing direct to Spain and we'll sail Newhaven to Dieppe and drive. Just waiting for the French announcement of the abandoning of the Test requirement before we book the Sailing Date, and then we can cancel the LFT Tests booked at Lloyds Pharmacy for 18th February!
Steve