For the last 17 years, I have been working overseas and considered as non-UK resident. I own a house which is rented out and also a 2-bed flat in London.  Both are mortgaged (maturing in 2018). What is the best available option for taking advantage of the capital gains tax exemption (before returning back to London) such as transfer of ownership, bearing in mind I am 69 years old and it’s impossible to re-mortgage at the same interest rate.  I also need to know how to verify my UK domicile status.  Should this be arranged through a solicitor?

As a non-UK resident, you will not have to pay UK capital gains tax on the sale of your UK assets. Since you went abroad before 1998, you are in a more favourable position regarding the UK capital gains tax (CGT) rules, although since you have been non-UK resident for over 5 consecutive tax years, it is not going to make too much of a difference. This exemption from UK CGT will apply to a sale before your permanent return to the UK. In respect of your domicile status, if you have a UK domicility of origin, even though you have been abroad for 17 years, and it appears you are planning to return to the UK, this UK domicility will remain with you.