EuroTrash

I've never heard that one before. Do you have a reference for it, please?
It seems very unlikely. France specifically doesn't make the "residence principale" issue a box ticking exercise - it takes all kinds of factors into account, which makes it harder for folks to play the system but equally, should make it fairer in that if a property genuinely is your residence principale, you don't have to worry about silly rules like this.
If you've lived in France at that address for 30 years and you leave in the month of May, I would be astonished if the fisc tried to say it was not your residence principale up until the date you left. And even beyond that, if your house is on the market but not sold when you leave France I think they normally allow you a reasonable time in which to sell before they regard you as liable to CGT - as long as you don't rent it out in the interim.
But would be interested to see a reference to the text in French law, it's always good to learn new wrinkles!

cator

There is no problem with the French side in selling without CGT. It is the UK tax that stipulates that any sale in the year of departure from France falls within the UK tax residence if in that year you did not stay in France for more that 186 days. This is because as I mentioned before, I have a house in the UK ( not rented) and under the DT treaty, I am considered as a dual resident inspite of having lived and worked in France for many years. This means that the sale must be after October so as not to trigger the UK tax residence ie less than 186 days in the UK..