Hi again.OPTION 1 - SELL AS NON-UK RESIDENT
Under new rules introduced with effect from 6 April 2015, non-UK residents who sell UK residential property may have to pay CGT in the UK which was not the case for disposals of such property prior to 6 April 2015. However, the value of the property on 5 April 2015 can be used as the "cost" of the property (instead of £410,000 in your case) which, together with the annual CGT exemption of £11,100, should pretty much cover your whole gain.
However, as you will not be selling until after your return to the UK for fear of incurring a CGT liability in the US, that option won't be open to you. I would have thought that there are reliefs in the US for periods when a property was the owner's main home. Take a look here
for information on the new rules for non-UK residents and gains made on UK residential property.OPTION 2 - ABSENCE RELIEF
Provided you have not owned another property which has been your main home since you moved abroad and you re-occupy the UK property before you sell it, you may be able to claim main residence relief for the period that you lived in the property and for the period that you worked abroad regardless of the fact that it was let. That would cover the whole gain and so there would be no CGT to pay. Take a look at CG65030 to CG65050 inclusive starting here
for information on the qualifying criteria for absence relief.OPTION 3
If you don't qualify for absence relief, you are will be able to claim relief from CGT as follows:
Total period of ownership to October 2015 179 months, occupied by you 145 months, let 32 months and vacant 2 months
Exempt gain £446,201 (£490,000 / 179 months x 163 months (145 + 18))
Letting period gain £38,324 (£490,000 / 179 months x 14 months (32 - 18))
Vacant period gain £5,475 (£490,000 / 179 months x 2 months)
Non exempt gain is £43,799 (£38,324 + £5,475)
Letting relief £38,324 (lesser of £40,000, £446,201 and £38,324)
Taxable gain £5,475 less annual CGT exemption £11,100 leaves no net taxable gain and, therefore, no Capital Gains Tax liability.
I have assumed that you reoccupy the property for one month before selling it. The gain for the period that you occupy a property as your main home is exempt from CGT as is the gain for the last 18 months of ownership regardless. Take a look at HS283 here
for more information on main residence relief and letting relief.
I hope this helps but let me know if you have any further questions.