I am a UK national and my spouse is from Argentina. We have been living in Europe for over 3 years and we are relocating back to the UK. I've been told by an immigration lawyer that as long as you have all your documentation to show that you have been exercising your EU treaty rights when you arrive at the airport they can give your spouse a stamp of residency for 6 months. Then once inside the UK, the full residence application has to be made.
If anyone has done this I would love to hear about it!