I know I'm like a broken record, but there needs be a more sensible / joined up approach to this; not just in the UK but across Europe. Science doesn't change at the border, but with everything in international diplomacy, each country makes it up as they go along. A common approach with exemptions, not just for air crew, but also for all key workers.
The map at the bottom of this ECDC webpage is a good colour coded indicator of regional variations.
https://www.ecdc.europa.eu/en/cases-2019-ncov-eueea
I'd argue that self isolation requirements should apply to the following:
Blue (zero cases) - Free travel... TLL for example
Yellow (less than 20 in 2 weeks) - free travel... LGW, NOC, OSL, RIX, FNC, LCA, HEL
Light orange (20-60) - recommend isolation, but not mandatory... LHR, MAN, DUB, FAO, MRS, TXL, CPH, FCO, ATH, VIE
Brown (60-120) - mandatory isolation with testing options... CDG, AGP, MLA, NCE
Maroon (120+) - lockdown... MAD, BCN, TFS, ACE, LPA