Hello, I'm Keith and happy to help you with your question.
Not many people realise that the ownership and subsequent disposal of landed property always gives a liability to CGT on the gain realised, but almost everyone is entitled to Private Residents Relief (PRR). Your current house would appear to be your sole or main domestic residence. On that assumption you are entitled to PRR which is at 100% of any gain. Furthermore that last 18 months of ownership do not count as you are deemed to be in residence even if you are actually living elsewhere and PRR is extended.
I do hope I have been able to set your mind at rest on this matter.