Hi again.UK CGT
You might refer to the notes in HS283
for information on the main residence and CGT.
You may be aware that non-UK resident owners of UK residential property who sell those properties after 5 April 2015 are potentially liable to CGT in the UK, whereas before 5 April 2015, they were not. As far as UK CGT is concerned you have several options to minimise your exposure to UK CGT as follows:
1 If you sell the property within 18 months of moving out, you will pay no UK CGT. The gain for the period that you occupy a property as your main home will be exempt from CGT as will the gain for the last 18 months of ownership regardless of the use to which the property is put, even letting. Letting will in fact help you if you keep the property for longer than 18 months after you move out as it will allow you to claim letting relief of up to £40,000 per part owner, the actual level being dependent on the facts and figures of the case. Example 9 in HS283 is worth a look to appreciate the effect it can have.
2 As you were sent to work in France by your employer, provided you do not buy a property in France and you re-occupy the property when you return to the UK before you sell it, you will qualify for main residence relief for the entire period of ownership of the property, even if it was let. Take a look at CG65030 to CG65050 starting here
for more information on that. Click on "Next Page" at the bottom right of each page to move to the next one.
3 As you may sell the property whilst non-UK resident, you might choose to use the 5 April 2015 value of the property as your "cost" for CGT purposes (as opposed to the actual cost) if it is to your advantage. There are a number of variations to this claim whereby you can either ignore the pre 6 April 2015 period of ownership or not depending on how if impacts on the taxable gain, if there is one. Take a look here
for more information on that.FRENCH CGT
I'm afraid that, since the current French government came to power, the rules around CGT in France and how it impacts on taxpayers with property in France or elsewhere has changed so often that I've lost trust in the information available on the internet as to how current it is. For that reason, you really ought to seek advice from a local accountant or tax consultant. I'd be surprised if there was no relief from French CGT to reflect the fact that the UK property has been your main home.
You might be able to get some advice through your employer if they are a large company with internal or external advisers who they use to manage and advise on their international tax obligations.
I hope this helps but let me know if you have any further questions.