Thanks for your question - I am Sam and I am one of the Uk tax experts here on Just Answer.
If you have been treated as not resident for UK tax purposes and make the sale before 05/04/2017 and return to the Uk after 06/04/2017 then you will have a NIL capital gain arising in the UK
If, however you are not treated as not resident for UK tax purposes - or return to the UK before 05/04/2017 and make the sale in this tax year or after, however its the timber that remains tax free rather then the increase of the sale of the land itself. unless you plan to reinvest into timber in which case there is consideration of business asset roll over relief.
Other than that there is just the annual exemption allowance which is currently £11,100 exempt.
Thanks for your response
No there is no taper relief this as abolished years ago as was indexation- as capital gains rates were lowered and I cannot comment directly on your tax position as we are an information service, and cannot give personal advsie without representing you (which we are not permitted to do as per our affiliation with Just Answer) - you will need to engage an accountant directly to help you find the most cost effective solution.
Yes as per double taxation - you will have only one tax position to consider, and if you are caught in both the Uk and France then credit is given for the tax suffered in one country against the others. But who remains responsible for you tax jurisdiction does all depend on when you sell and when you leave France/return to the UK (where the placement wasmade should have no bearing)
If you could also allow me to deal with each of your posts at a time, each time I go to reply you add another piece of information and I have to rewrite my reply. (So If I have missed anything please do advsie)
Then there is no business asset roll over relief either if you do not own the land, - its just a straight forward capital gains position from the UK perspective