Then you will not be allowed to claim the full amount for Private residence relief.
Because you left the UK you have to know what the house was valued at on 5 April 2015. You paid £260k back in 2005 but the gain is just assessed from 5 April 2015.
Once you know that then you can apply the tax free allowance amount. From 2015 to 2016, non-residents who dispose of a UK residential property will be liable to Capital Gains Tax and, in most cases, will be able to claim the Annual Exempt Amount in the same way as for UK residents.
The first £11,100 of the gain is not taxed. Then you can claim a portion of the Private Residence Relief based on your actual use time.
Example You make a gain of £120,000 when you sell your home, which you owned for 12 years. You lived in the whole property for 6 years, then you let it out in full for 6 years.
You get Private Residence Relief for the time you lived there (6 years). You also get relief for the last 18 months you owned the property, even though you weren’t living in it.
This means you get Private Residence Relief for 7.5 of the years (62.5% of the time) you owned the property.
You get Private Residence Relief on the same proportion (62.5%) of your gain. This means you won’t pay tax on £75,000 of the gain.
The remaining 37.5% (£45,000) of the gain not covered by Private Residence Relief is your chargeable gain.
I cannot tell you a specific tax for you because you have not said what the house valued for in 2015.
You also have letting relief that can be up to £40,000.
Unless the property shot up in value form 2015 till you sell you may not have any tax.