IFR approach with missed approach to an IFR alternate in Alps winter after 600nm leg, ahem that sounds like James (Peter) Bond 
VFR alternates, Annemasse & Sion, worst case cloud-break on Geneva IAP and turn right to Annemasse or follow the lac and turn right/left to Sion
IFR alternates, Annecy & Chambery, if they are not good, I would fly back to the UK rather than ending up in Geneva or getting wet inside the Alps
I am sure you can claim all the 4 have airside customs setup and all have restaurants or crew lounges airside 
Thanks. I will plan both Sion and Annecy.
My plan is to check the Annecy webcam before departure, but is there some local site with more data?
Peter wrote:
What would be a good alternate for Aosta, in case it is found to be overcast?Obviously there is a number of them in SE France but what about getting similar weather? Also I would much prefer one with a setup where everything can be done airside, due to CV19 issues with returning to the UK from France, so I can claim I never entered France.
Turin maybe?
For an alternate, and given I won’t be going to Aosta after diverting there (because a couple of days later the wx turns crap again) I would want one on the way back. Actually I could fly to Aosta and turn around and fly all the way back to Shoreham, ~7hrs TT, but the fuel would be a little tight especially looking at the winds.
Peter
one last suggestion, and one that I have used a couple of times, if the approaches “within the mountains” ie Aosta, Sion, Annemasse and Annecy are all clagged in, then head a bit further back to Lyon Bron LFLY. Its in flat country well away from the alps, very simple IAPs, and very very GA friendly.
And also has a good restaurant! Though not airside.
Peter wrote:
I will plan both Sion and Annecy.
Check France closing borders.
You should be able to refuel even if a country is closed. We did this one before and there are some data points. One exception is Alderney EGJA which prohibits any “full stop landing”:
AIRCRAFT MAY NOT COMPLETE
A FULL STOP LANDING WITHOUT RECEIVING PPR AND/OR SUBMITTING THE
COMPLETED DOCUMENTATION FOR PUBLIC HEALTH AS REQUIRED.
I have not seen this for any other airport. There are airports which cannot be filed as Alternate, however.
Asking for someone else, I have a question on airspace access under VFR on the following IFR routes
Obviously I know the UK end.
In France, the same route can be flown because below FL120 it is generally Class E, and above FL120 France bans VFR in most of the Paris region.
What are Switzerland and Italy like?
In the canyons you fly VFR anyway so south of SPR nobody will be watching.
Italian airspace is uncontrolled in that region. Between the Jura and SPR, Geneva Delta on 119.175 above FL075 for crossing, or fly uncontrolled below FL075 with flight following from Geneva Info 126.35.
