Can anyone tell me how any tax liable will be calculated on the sale of my rented property?
You will pay Capital Gains Tax on the sale unless you have lived in it recently. You could move in for a year or two and avoid that tax. Anyway, why sell it? Keep it rented and at least you will have a hedge against inflation (assuming you plan a long retirement). If you can reduce the mortgage you’ll get a better yield. In my opinion the worst thing you could do is sell it. Selling costs then tax on the gain and then inflation diminishing the worth of what’s left. I too plan (in 6 months) to fund my retirement from property income but this will be from keeping rented property rather than selling it.