There are special rules if you work overseas (and rules for working away in the UK)
This blog focuses on working overseas. The important thing to make sure you keep good records and tell your accountant!
Office/employment outside UK
TCGA92/S223 (3) (b)
You may allow relief for a period of absence of any length throughout which an individual worked in an employment or office all the duties of which were performed outside the United Kingdom, or a period of absence throughout which the individual lived with a spouse or civil partner who worked in such an employment or office if the conditions set out in CG65046 are fulfilled.
All of the duties of the employment must be performed outside the United Kingdom. You can ignore any return to the United Kingdom for holidays, but you should not ignore any duties which are in practice performed in the United Kingdom even if they are only incidental to the main duties performed outside the United Kingdom.
https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg65040
Condition A
Before the period of absence there must be a time during which the dwelling house was the individual’s only or main residence.
Condition B
After the period of absence there must be a time during which the dwelling house is the individual’s only or main residence (if within S223 (3) (a), (b), (c) or (d))
Use of residence during period of absence
It does not matter how the residence is used during a qualifying period of absence. For example, it may be let without any loss of relief.
 https://www.gov.uk/hmrc-internal-manuals/capital-gains-manual/cg65050
