Sale of the property purchased before becoming UK tax resident

[seeker2122]

I sold my foreign property in a market with highly volotile FX rates, so timing in calculation is important here.

Now as I am submitting my tax return I am trying to work out right way of calculating capital tax gains. Here are three events with some references:

Time Amount in local currency GBP equivalent
Date of purchase of the property
A
X

Date of me becoming UK tax resident
B = unknown but can be assumed A as latest valuation date
Y

Date of sale of the property
C
Z

How do I calculate my capital gain? Z - Y or Z - X? Or maybe C - B (or A?) using exchange rate at the date of sale?

Also, if my capital gains are negative, i.e. losses. Can I offset them against my employment income?

Thank you very much in advance for any piece of advise on this.